AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 314 AM CDT FRI APR 28 2000
SYNOPTIC SCALE...RATHER SLUGGISH OVERALL PATTERN THIS PORTION
OF THE WORLD WITH EAST COAST TROUGH...PLAINS RIDGE AND WEST
COAST TROUGH. OVER NEXT 48-72HRS EASTERN SYSTEM FORECAST TO
EDGE EASTWARD AS REAR JET ROTATES TOWARD BASE OF TROUGH WHILE
WEST COAST TROUGH IS PUSHED EAST THROUGH THE PLATEAU AND
WEAKENS. MEAN RIDGE APPEARS TO BE SITUATED OVER THE PLAINS
WHICH ACCOUNTS FOR SOME OF THE WEAKENING. COLD POOL AT BASE
OF THIS WESTERN TROUGH PROGGED TO CUT OFF AS UPPER LOW OVER
THE FAR SW PLAINS ABOUT MON...ITS THAT TIME OF YEAR.
REGIONAL SITUATION AND FORECAST...WHILE SURFACE FEATURES
REFLECT THE BUILDING ANTICYCLONE OVER THE NORTHERN PLAINS AND
SCNTRAL CANADA..ALOFT THE FLOW IS DOMINATED BY SLOWLY
PROGRESSING NORTHERLY JET ON BACK SIDE OF EASTERN TROUGH.
SOME TROUGHINESS SEEN IN MID LEVEL FLOW ALTHOUGH JET DYNAMICS
SUGGEST MORE SUBSIDING THE RISING TO REAR OF CORE. LOW
LEVELS ALSO QUITE DRY SO CLOUDS ACROSS MINN AND IOWA ARE
HAVING TOUGH TIME HOLDING TOGETHER.
MODELS SUGGEST MAIN CLOUD BAND WILL SLIDE ACROSS CWA THIS
AFTERNOON THROUGH TONIGHT. ACARS DATA THIS MORNING INDICATES
RISE TOWARD 70DEG QUITE LIKELY UNLESS CLOUDS TEMPER THINGS.
MID LEVEL LAPSE RATES ALREADY STEEP AND FORECAST TO CONTINUE
THAT WAY PRIOR TO MID LEVEL TROUGH PASSAGE TOWARD EVENING.
THUS WILL HOLD MINIMAL CHANCE OF RW/TRW LATE AFTERNOON AND
EVENING FOR CWA.
WITH SURFACE ANTICYCLONE MOVING BY TO NORTH SAT/SUN EXPECT NE
AND EAST WINDS WILL HOLD TEMPS DOWN BELOW AVERAGE DURING THIS
PERIOD. WILL ANGLE MORE TOWARD FWC NUMBERS TODAY THEN
GENERALLY FOLLOW THE TREND THEREAFTER. WITH UPPER LOW
PROGGED TO CUT OFF WELL TO THE SW LATER IN WEEKEND RETURN OF
MOISTURE SHOULD BE SLOW EARLY NEXT WEEK MUCH LESS ANY PRECIP.
WILL BACK OFF PRECIP FOR SUN AND EVEN MONDAY FOR ALL BUT FAR
WESTERN CWA COUNTIES. KML
.CHI...NONE
AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 247 AM PDT FRI APR 28 2000
WITHOUT LCL COMMS/LAN. MAIN CONCERNS ARE WITHIN NEXT 24 HRS. MDL
INITIALIZATION PREFERS AVN/ETA PER ACARS/IR IMAGERY... YET SUBTLE
DIFFERENCES BTWN 2. AVN 1C COOLER AT 5H AND 1-2 DEGREES SLOWER MOVG
TROF AXIS INTO PAC NW THIS EVE. APPEARS SMALL...YET FACTORS INTO
STABILITY INDICIES THIS AFTERNOON/EVE...SPECIALLY WITH INCRG
SUNBREAKS AND LOW LVL HEATING. ETA STABLER WITH CONV TEMP 54 TO AVN
44. PREFER ETA GIVEN LACK OF UPR FLOW AND AVN'S COLDER BIAS. RE:
CONVECTIVE POTENTIAL...PER ETA, MNML SHEAR AND LACK OF JET DO NOT
FORESEE LAST NIGHT'S NOTION OF TSTORMS. ADDITIONAL LIFT IN CONV ZONES
WITH MESOETA LI'S +7/+7.5C THERE, THUS ADDING TSTORMS THERE. PER AMT
OF COLD AIR, ADDING ICE PELLETS TO ZONES AND DROPPING -SN LVLS 1K FT
IN MTNS. NEXT CONCERN IS AMT OF SNOW IN MTNS TONIGHT. PER MM52-D .1-
.15 IN/HR LIQ PCPN OVR NRN CASCDS LATE AFTERNOON/TONIGHT WITH FORCED
LIFT IN WSW 85H FLOW. XPCT SNOW ADVISORY CONDS NRN CASCDS TONIGHT...
YET GIVEN TIMING...HAVE TO LET DAY SHIFT TO ISSUE. ELSEWHERE UP TO 6
INCHES. ONWARD...DIRTY RIGE BLDG SAT/SUN...WITH SERIES OF SHORT
WAVES WITH STG WAA RIDING ACROSS TOP OF RIDGE INTO CWA...POSING
THREAT -RA CST/OLYMPICS THRU SUN. WILL KEEP INTERIOR DRY AND WARMER.
.EXTNDD...NOT A LOT OF CONFIDENCE IN MDLS GIVEN RETURN OF SPLIT FLOW.
DO NOT LIKE MRF'S BYD 84 HRS...WITH 96 HR MELD OF THE SPLIT
UNREASONABLE. SUSPECT FLOW TO ACTUALLY RMN SPLIT WITH SRN BRANCH
ENERGY RMNG S 40N AND CYCLOGENSIS OFF CA CST. YET TIL THEN...SWLY JET
SPRDG NE INTO B.C. WITH ENERGY SKIMMING PAC NW MON/TUE...THUS CHC -
SHRA SHOULD COVER IT. IF NOTION IS ON... MAY EVEN BE A DRY PD THEN.
QUERCIAGROSSA
UIL 933 SEA 741 OLM 731
.KATX...VCP21/CSR21...OPERATIONAL
.SEW...SCA EVERYWHERE XCPT CENTRAL STRAIT JUAN DE FUCA
N