A collection of weather report deciphering information downloaded from CompuServe AVSIG on 5/23/90: ------------------------------------------------------------------------------- [76703,730] RAREPS.TXT 03-Apr-90 8485 Accesses: 71 Title : Condensed Guide to Reading Radar Reports Keywords: RADAR REPORTS SD DECODE DECODING WEATHER WX NWS RAREP RAREPS EMI How to read NWS Radar Reports (SDs), adapted from a NWS publication. Text file; use the READ or DOWNLOAD commands as you wish. Includes address for radar site plastic map overlays. You might also check out RADAR.OBS in this LIB for more info if needed. Decoding Radar Reports If any precip echoes are present, a radar report consists of two sections: an SD section and a "digital" section. The SD section comes first, and presents radar data in an azimuth-range ("heading-distance") format. The digital section presents a more detailed description of the echo locations and intensities using a grid system. The two report sections are separated by a ^ symbol. The SD section can be broken down to nine basic parts. 1. ECHO CONFIGURATION. One of the following will describe the configuration of the precip echo. AREA An area of related echoes LN A line of convective echoes CELL(S) Isolated convective echo or echoes LYR An elevated layer of stratiform echoes FINE LN A fine line, a narrow nonprecipitation echo pattern EYE A hurricane or tropical storm eye CNTR A hurricane or tropical storm center SPRL BAND AREA A hurricane spiral band area 2. AREAL COVERAGE. How much of the described location is covered. It's a one- or two-digit number with 10 meaning total coverage. 3. PRECIPITATION TYPE. This is the easy part, if you're used to SA reports. The symbols used are: R Rain RW Rain shower ZR Freezin rain ZRW Freezing rain shower S Snow SW Snow shower L Drizzle ZL Freezing drizzle IP Ice pellets IPW Ice pellet shower A Hail T Combined with one of the above to indicate presence of thunder 4. INTENSITY. More symbology: - Weak (light precip) Moderate (moderate precip, the default) + Strong (heavy precip) ++ Very strong (very heavy precip) X Intense (intense precip) XX Extreme (you get the idea) U Unknown 5. INTENSITY TREND. Think how much space these symbols save: - Decreasing NC No change + Increasing NEW Newly developed 6. ECHO LOCATIONS. Position relative to radar location. Directions are in degrees from true north, distances are in nautical miles. Each location is described by one direction, a slash (/), and one distance. For example, a location 103 nm SW of the radar site would be described as 225/103. If the area covered by echoes is irregularly shaped, you'll see several locations described; these correspond to pertinent points on the area's perimeter. If the echoes are arranged in a line or rectangular area, the locations describing the area's axis will be accompanied by a reported width. When describing a circular area or isolated cell, the location corresponds to the center of the covered area, and the width is included. 7. MOVEMENT. Type of echo moving, direction in tens of degrees, and speed in knots. The echo is described as A (area), C (cell), or L (Line). For example, an area moving from the northwest at 25 knots would be listed as A3125. 8. ECHO TOPS. Height in hundreds of feet of either echo tops ("TOP") or maximum tops ("MT"). "U" before the height means the echo tops are uniform. For example, 37,000-foot maximum tops 57 nm east of the radar site would be listed as MT 370 AT 90/57. ["AT" is not a contraction - just "at."] 9. REMARKS. The last part of the SD section of the report. HOOK Hook echo. Accompanied by its location. HAIL Radar-indicated hail, with location(s). LEWP Line echo wave pattern, with defining locations. VAULT Echo-free vault or bounded weak echo region, with location. MALF Mostly aloft precip. See BASE, below. PALF Partly aloft precip. See BASE. BASE Base of precip aloft, with height in hundreds of feet. Used with MALF and PALF, and also LYR (layer). MLTLVL Melting level, with height in hundreds of feet. You may also see these contractions, frequently with nothing else in the report: PPINE Equipment operational, no echoes observed. PPIOM Equipment OTS for maintenance until listed date-time. PPINA Observation not available. May be followed by expected service resumption date-time. ROBEPS Radar operating below performance standards. ARNO A-scope or A/R (azimuth-range?) indicator OTS. RHINO Height data unavailable. The Digital Section After the up-caret (^) at the end of the SD section of the radar report comes the digital section. Using data from this section in conjuction with a grid map for the area surrounding the radar site, you can precisely plot the locations and intensities of radar echoes. Even without a grid map, you can get valuable information from this section. The digital section usually describes only those echoes within a radius of 125 nm of the radar site, whereas the SD section can describe radar echoes from further away. The grid contains boxes about 22 nm on each side. It's based on what's called the "Limited Fine Mesh I" grid; to the joy of Montana, Wyoming, Colorado, and Arizona residents, correct north-south orientation is at 105 degrees west longitude. East and west of 105 degrees, the grid is skewed with respect to true north. It's a pretty hefty skew in the northeastern US. Maps for all current U.S. radar reporting sites can be found in a publication entitled NWS Radar Code User's Guide (from which this text is adapted). NWS also has paper copies and plastic overlays for individual sites; the paper copies are free (or were, in 1981) but they'll charge you for the reusable overlays. For details write to: National Weather Service Chief, Technical Procedures Branch, W111 8060 13th Street Silver Spring, Maryland 20910 Each box in the grid can be identified by two letters: the first indicates the row, and the second indicates the column. Rows are lettered from north to south and columns from west to east. The radar site itself is always in box MM. The maximum observed intensity is reported for each grid box containing echoes of moderate or greater intensity. Light intensity precip covering less than 20 percent of a grid box goes unreported. The code numbers used are probably familiar to you: 0 No echo, no precip 1 Weak echo, light precip 2 Moderate echo, moderate precip 3 Strong echo, heavy precip 4 Very strong echo, very heavy precip 5 Intense echo, get outta the way 6 Extreme echo intensity, don't even think about it 8 Unknown, believed heavy 9 Unknown, believed light The digital section consists of one or more data groups, with a space separating one from the next. Each group describes echoes on one row of grid boxes, and consists of a two-letter box identifier and one or more digits for echo intensities. The box corresponds to the most westerly box on that row with a reportable echo; the first digit is that box's echo intensity, and any following digits describe the intensities of precip in succeeding boxes on that row. For example, the data group MI22013 represents level 2 precip in boxes MI and MJ, no precip in box MK, level 1 in box ML, and level 3 at the radar site, box MM. READY FOR AN EXAMPLE? Okay, here's one: NYC 1830 AREA 1RW3R-/NC 338/120 153/150 260W C2025 MT 220 AT 102/72 PTCHS R ^HL221009 IK2221111 JJ11211111 KJ1111121 LO121 MN1102 NI11110010229 OK12 PK111 QK11 RL9 SQ9= Now, if I understand what I've been writing, here's what that report says: New York City radar report issued at 1830 UTC. An area of echoes consisting of one-tenth coverage in rain showers, and three-tenths coverage in light rain, unchanged in echo intensity. The area stretches from 120 nm north-northwest to 150 nm south-southeast of NYC, and is 260 nm wide. Cells are moving from the south at 25 knots. Maximum tops are 22,000 feet at 72 nm east of NYC. Patches of rain. Precip is moderate in grid boxes HL and HM, light in HN, nonexistent or very light in HO and HP, and unknown but believed light in HQ. Etc., etc. Hope all the above is helpful! Please let me know if the text can be corrected or improved in any way. Clay Cromley [76703,730] [73667,3552] WXDECO.TXT 03-Jan-90 3783 Accesses: 195 Title : WEATHER DECODE RADAR REPORTS SA Keywords: WEATHER DECODE RADAR REPORTS SA Aviation weather report help selection combined with excerpts from David Sankey's outstanding treatise on radar weather reports. An effort to ease the pain of decoding SAs and Radar Observations -- Tim Healey Press for next or type CHOICES !read SA & RADAR DECODER SA - Surface observation ======================== Weather & Visbility Codes Prefixes Suffixes ------------------------- --------- -------- hAil drizzLe Blowing shoWers Dust saNd freeZing + heavy Fog Rain - light Ground Fog Snow ++ very heavy Haze Snow Grains Ice Crystals Snow Pellets Ice Fog Thunderstorms Ice Pellets spraY smoKe freeZing Rain shoWer Cloud Abbreviations Ceiling Prefixes ------------------------------------- ---------------- CLR CLEAR: <10% sky cover E-Estimated SCT SCATTERED: 10-50% sky cover M-Measured BKN BROKEN: 60-90% sky cover W-Indefinite OVC OVERCAST: >90% sky cover V-Variable - THIN (prefix) X OBSCURATION: sky obscured -X PARTIAL OBSCURATION: sky partially obscured Example: LGA SA 1352 15 SCT M25 OVC 1R-F 132/58/56/1815G21/993/R28LVR20 LGA = LaGuardia SA=regular hourly Surface observAtion [SP=special] 1352 = time of observation 13:52 UCT [EDT+5; EST+4] 15 SCT = scattered clouds 1500' above ground(airport) elevation M25 OVC = overcast clouds measured at 2,500 AGL 1R-F = visibility 1 statute mile, with restriction to visibility identified as light rain and fog 132 = barometric pressure in millibars=1013.2 58/56 = temperature / dew point in F 1815G21 = wind from 180 degrees magnetic at 15 knots; peak gust 21 R28LRV20 = runway 28 left visual range 2000 feet Radar Observations =================== Format: Station ID/time/location intensity azimuth and range/movement/ tops/precipitation type-intensity trend/remarks/end Example: NYC 1930 AREA 2 TRW++/+ 297/130 152/115 160W C2620 MT 300 AT 254/39 HAIL REPORTED THIS CELL NYC RADAR 1930 UCT; AREA OF ECHOES 2/10 COVERAGE, VERY HVY THUNDERSTORMS FROM 297 DEGREES/130 NM TO 152 DEGREES/115 NM; AREA IS 160NM WIDE;MAX TOP 30,000' AT 245 DEG/39NM; RMKS PLAIN LANGUAGE; Intensity Decoder ----------------- Level Echo Intensity Precip Intsy Rainfall Rate ----- -------------- ------------- ------------- 1 Weak None or light <.1-.2 2 Moderate Moderate .1-1.1 3 Strong Heavy .5-2.2 4 Very Strong Very Heavy 2.2-4.5* 5 Intense Intense 4.5-7.1* 6 Extreme Extreme >7.1 in/hr *= only in convective situations 8 Unknown but associated with severe wx 9 Unknown Abbreviations ------------- HOOK - signature "tail" usually associated with tornadoes HAIL - radar indicated hail LINE - echoes are in a line LEWP - Line Echo Wave Pattern - wavy line FNLN - FiNe LiNe; narrow non-precipitation echo pattern BWER - Bounded Weak Echo Region - echo free vault within a cell ALFT - precipitation ALoFT MALF - Mostly ALoFt precipitation PALF - Partly ALoFt precipitation MLVL - Melting LeVeL; radar detection of melting of frozen precip PCLL - Persistent CeLLs SLD - SoLiD areas of 80% or more PPINE - equipment normal; No Echoes OM - inOp or out of service for Maintenance NA - observation Not Available NS - equipment normal; No Significant echoes ROBEPS Radar Operating BElow Performance Standards ARNO - Azimuth Range indicator iNOperative RHINO - Radar Height Indicator iNOperative [74146,3552] 2METCO.DAT 10-Nov-89 8032 Accesses: 140 Title : Explanation of the contractions used in Wx Reports Keywords: FORECAST EXPLANATIONS EXPLANATION OF CONTRACTIONS USED IN FEs METEOROLOGICAL CONTRACTIONS CONTRACTIONS USED IN FORECAST DISCUSSIONS - 2ND ED. The NWS uses contractions in FEs (designated FPUS3 on some systems). The list below supplements a previous contribution (METCON.DAT) by the same contributor. Additional supplements will be made, if appropriate. CONTRACTION MEANING/USE INV Inversion; generally refers to an increase in temperature aloft, contrary to the usual decrease with ascent. LID Describes an inversion strong enough to prevent or retard convection. Frequent forecast problem is to determine if daytime heating will overcome an existing LID, releasing potential instability and producing thunderstorms. CAP same as LID. CONV Convection; atmospheric motions which are predominantly vertical; in common usage, thunderstorms. CONV Convergence; the contraction of a vector field; in usual context, the tendency of air currents to flow toward one another. DIV Divergence; the expansion or spreading out of a vector field; commonly, the tendency of air currents to flow away from one another. THKNS Thickness; a statement of the distance between two levels of geopotential pressure (such as 1000mb, 850mb, 700mb, 500mb, etc.); a decrease in thickness yields a decrease in the ability of the atmosphere to retain heat. THKNS COOLING Cooling resulting from decreasing thickness. MODELS Much meteorological research involves computer modeling of the atmosphere and its properties, for use in fore- casting. Several national and international centers are involved: NMC National Meteorological Center (U.S.) NCAR National Center for Atmospheric Research (U.S.) UKMET United Kingdom Meteorological Office ECMWF European Centre for Medium-Range Weather Forecasting CAN Environment Canada The models and their products are referred to by either the name of the model, or of the center using it. A partial list follows: NMC: AVN (Aviation); NGM (Nested Grid Model); LFM (Limited Fine Mesh); PE (Primitive Equation); SPEC (Spectral Model); MRF (Medium Range Forecast) UKMET: same ECMWF: same Env.Canada: RFE (Regional Finite Element model) In addition, the Air Force and Navy both have their own models, as does the National Hurricane Center. The context in which these terms are used in FEs is usually to note variances between the models; often a balance must be struck. PW Precipitable Water; a value computed from surface and RAOB data; a statement of the quantity of water available for precipitation in a given column of atmosphere. Actual amounts of precipitation may exceed PW because of the effects of con- vergence (i.e. concentration of PW from nearby areas). RAFS Regional Analysis and Forecast System; NWS forecast offices have this locally-run computer program to diagnose frontal positions, temperature and wind discontinuity, moisture con- vergence, etc. on an hourly basis, when required. Hence, an important new tool in short-range forecasting. MOS Model Output Statistics; numerical forecast data derived from statistical massaging of gridded model output. PP Perfect Prog; another form of MOS. POP Probability of Precipitation; one element of MOS JET Jet stream JET MAX=a pocket of high speed winds within the general jet stream JET STREAK=usually observed in GOES loops, an area of clouds at jet stream level moving faster than surrounding clouds; consider- ed an indicator of a JET MAX, it has particular significance for severe weather forecasting. VORT Vorticity; a vector measure of local rotation in a fluid flow; as used in meteorology, vorticity means vertical motion. VORT LOBE=a "glob" of vorticity; c.f. VORT CNTR; VORT MAX (See METCON.DAT) VORT LOBES frequently rotate around closed low centers at the 500mb level. CHANNELIZED VORT=Refers to the tendency for some closed lows to con- solidate vorticity around them into relatively narrow bands. LAPSE RATE the rate of temperature decrease with ascent. The lapse rate is generally classified into two types: dry adiabatic and moist adiabatic. The dry adiabatic rate is approximately 5.4 degrees F per 1000 ft. The moist rate is less, and generally around 3.5 degrees F per 1000 ft. LDIS Lightning Detection and Indication System; a near real-time system detecting and displaying cloud-to-ground strokes. HODOGRAPH A chart depicting vertical distribution of the horizontal wind; commonly used in forecasting tornado probabilities. K VALUES a stability index used in severe weather forecasting. LCL Lifted Condensation Level; the level at which a parcel of moits air lifted dry adiabatically would become saturated. LFC Level of Free Convection; thelevel at which a parcel of air lifted dry adiabatically to saturation and moist adiabatically thereafter first becomes warmer than the surrounding air. At this level, convection will support itself without applica- tion of other forces. HT Height; generally refers to geopotential heights at standard pressure levels (1000mb; 850mb; 700mb, etc.); normally sta- ted in decameters. HGT same as HT HT RISES=Height rises; observed or forecast increases in geopotential heights of standard pressure levels. HT FLS Height falls; opposite of HT RISES HFC Height fall center; observed or predicted position of maximum height falls over a stated period (12hr, 24hr, etc.); signifi- cant in forecasting position of surface low development or intensification; usually applies to changes in HT at 500mb. EFP Extended Forecast Period; three to five days ahead FP Forecast Period; up to thirty-six hours ahead RDGG Ridging DRY SLOT Refers to an area in the flow around a low pressure area in which dry air has been entrained into an otherwise moist atmosphere. TELECONNECTIONS=System for evaluating model forecasts against past statistical trends and patterns; deviation of the current output from past patterns often indicates a flaw in the current forecast pattern CATGY Category; MOS probabilities, temperature, wind speeds, etc. are bracketed in categories; example: 20% POP=Chance or slight chance, but 50% POP=Likely. ITCZ Inter-Tropical Convergence Zone IR Infra-red; one type of image sensing on GOES VIS Visual; another type of image sensing on GOES WV Water vapor; another type of sensing on GOES which produces a visible image of water vapor not in the form of clouds. =