Precipitation-related forecast discussions

SRN AND SERN PTN OF VORTEX OVER WESTERN DAKOTAS SPINNING AN AREA OF SNOW INTO WRN IA THIS MORNING. SNOW SUPPORTED BY SOME WARM ADVECTION IN MID AND LOWR LEVELS ALTHO WIND FIELD STILL MODESTLY LIGHT. NEW NGM/ETA RUNS AGREE QUITE WELL IN SEQUENCE OF EVENTS TNGT AND EARLY FRI. LOOKS LIKE DEFINED THETA-E RIDGE WL BE MOVG ACROSS NRN/CNTRL IL TNGT STIRRED BY APPRCH OF HI LVL JET WITH ASSOCD DIVERGENT POOL. THIS JET EMERGES UNDER DAK VORTEX AND LOOKING AT ACARS THIS MRNG THERE IS A 80+ JET RUNNING ACROSS SRN WYOMING ALREADY. THUS HAVE SOME CONFIDENCE THAT COUPLING OF LWR LVL THERMODYNAMICS AND HIER LVL DYNAMICS WL OCCUR. NEW MOS APPARENTLY CAUGHT ON TOO AS POPS WERE BOOSTED QUITE A BIT FOR TONIGHT LCLLY. THREAT WL BE TNGT SO THAT PD WL BE ADJUSTED. DOING IT NOW TO LEAD INTO AFTN PKG WITH MINIMAL SURPRISES. IN ADDITION...ORD ACARS ALSO SHOWS VERY STEEP LAPSE RATES IN NERN IL THIS MORNING. SCT SNOW SHOWERS SEEN OVR LK MI OCNLY COMING ASHORE AND THIS TREND SHD CONT THIS AFTN NR LKSHORE. LOCAL FCST WL BE UPDATED TO REFLECT THIS TOO. WITH SUCH STEEP LAPSE RATES TEMP CLIMB WL BE SLOW AND CURRENT FCST LOOK OK TO HOLD THINGS IN THE 30S.

KML

UPR LO HAS BOTTOMED OUT NR CALIF/SRN ORE CST THIS MRNG. DEFORMATION BAND TO N AND NE OF LO PRODUCG SM PCPN OVR SRN PART OF WA AND KATX RADAR SHOWS BAND OF SHWRS MOVG VERY SLOWLY N OVR SW WA MAINLY LEWIS COUNTY SWD. NEW ETA MOVS UPR LO CNTR INLND ACROSS NRN CALIF TO NRN NV BY 36 HRS. THUS DON'T BELIEVE MSTR WL MOV MUCH FARTHER NWD OVR WRN WA TDA...PROBABLY ABT THE SAME AS YESTERDAY AFTN/EVE. ACARS SOUNDINGS ARND SEATAC SHOW NORTHERLY WINDS UP TO ARND 6000FT AND THEN MORE ERLY. SO SOME CONVECTION POPPING ON CASCADES THIS AFTN/EVE COULD DRIFT OFF INTO FOOTHILLS...BUT MAIN PCPN WL BE SW PART. CURRENT FCSTS ON TARGET. NO BIG CHGS.

ART

THE 500MB FLOW ACROSS THE PACIFIC IS NOT TYPICAL OF EARLY TO MID WINTER AS IT IS NEAR IMPOSSIBLE TO IDENTIFY SPECIFIC JET STREAMS. GOES 9/GMS COMPOSITE SATELLITE LOOP SHOWS 7 DISTINCT RATHER CUT OFF LOOKING LOWS ACROSS THE PACIFIC/BERING SEA REGION AT 06Z. RUN-TO-RUN MODEL CONTINUITY/MODEL CONSISTENCY IS VERY POOR WITH LARGE AVN/MRF ENSEMBLE SPREADS AS MODELS HAVE DIFFICULTY INITIALIZING DETAILS IN RELATIVELY DATA VOID PACIFIC IN UNSTABLE REGIME. AS A RESULT THE FORECAST NEW YEARS DAY AND BEYOND IS JUST ABOUT ANYONES GUESS WITH DETAILS IMPOSSIBLE TO FORECAST AT THIS TIME. .WESTERN WASHINGTON...00Z KUIL SOUNDING SHOWED 6KFT THICK UNSTBL/MOIST BOUNDARY LAYER WITH 10-20KT LOW LVL SWLIES. WARM RA GENERATED IN THIS LAYER IN ONSHR FLOW HAS PRODUCED A FEW HUNDREDTHS PCPN COAST AND A HUNDREDTH AT KSHN. RADAR BEAM GOING RIGHT OVER THE TOP. ACARS SOUNDINGS ABOUT 00Z SHOWED LAYER ONLY 3KFT THICK IN THE INTERIOR WITH 07Z ACARS SOUNDINGS SHOWING LITTLE CHANGE IN THERMAL REGIME BUT DECREASED LOW LEVEL ONSHORE WINDS. EXPECT LITTLE IN THE WAY OF PCPN IN THE INTERIOR WITH LIGHT DRIBBLES CONFINED TO COAST AND CHEHALIS GAP EARLY THIS MORNING TIL LOW LEVEL FLOW COMPLETES ITS TRANSITION TO OFFSHORE. BREAKS IN STRATUS DECK EVIDENT TONIGHT IN THE INTERIOR SO WILL CONTINUE PREVIOUS FORECAST TRENDS FOR PARTLY SUNNY CONDITIONS THIS AFTERNOON EXCEPT IN S INTERIOR VALLEYS WHERE MOISTURE WILL REMAIN TRAPPED...

ALBRECHT

COLD FRONT EXTENDED FROM NRN LM ACRS SRN WI AND NRN IL AT MIDNIGHT. ADAP SHOWING WK MOISTURE CONVERGENCE ALONG PREFRONTAL TROF FROM NE IL TO NRN MO. EVE SOUNDINGS AND LATEST ACARS SHOW AMS ONLY SLIGHTLY UNSTABLE AND APPEARS WITH VERY WK FORCING FRONT WL PROCEED ACRS

IL ON THE DRY SIDE TODAY. TROF OVER LWR MS VLY LAST COUPLE OF NIGHTS HAS SHIFTED OFF TO THE EAST A BIT TONIGHT. COMPOSITE RADAR LOOPS SHOW PRECIP HAS BEEN DECREASING AND ALSO MOVING OFF TO THE EAST WHICH IS IN LINE WITH THE ETA FCST SO NO FURTHER PROBLEMS EXPECTED FOR US FM THIS SYS. WL CONT WITH MOSTLY SUNNY FCST NW AND PARTLY SUNNY SE WHERE MORE CU SHD FORM SHILE WAITING FOR DRIER AIR TO ADVECT INTO LOW LVLS.

DRY WX SHD CONT ACRS STATE TONIGHT. MODLES FCSTG SOME HI CLOUDS TO SPILL OVER RIDGE INTO STATE. ALSO, AS H850 HIGH SETLLES SEWD INTO SRN PLAINS WARM/MOIST ADVECTION IN RETURN FLOW WL SET UP POTENTIAL FOR SOME OVERRUNNING THUNDERSTORMS TO DVLP OVERNIGHT AND FRI OVR MN/IA. H850-300 THKNS SUGGESTS ANY STORMS WHICH DO DVLP WL PROPAGATE SSE STAYING WEST OF FA WITH JUST SOME HI CLOUDS REACHING IL.

FCST SOUNDINGS INDICATE THAT SIMILAR FAN/FWC FCSTS WL BE CLOSE THRU FCST.

TAYLOR

SHORT TERM FOR NORTHEAST AND NORTH CENTRAL COLORADO: STILL LOTS OF LOW LEVEL MOISTURE PRESENT AS EVIDENT BY BROKEN SC ACROSS AREA. HAVE YET TO REACH CONVECTIVE TEMPERATURE...WHICH WOULD HAVE GOTTEN SHOWERS AND A FEW STORMS DEVELOPING. LATEST ACARS AND GOES SATELLITE SOUNDINGS STILL INDICATING INVERSION AT 600MB...WHICH WAS HELPING TO PUT A CAP ON CONVECTION. WATER VAPOR LOOPS INDICATE SHORTWAVE OVER EASTERN WYOMING SLIDING SOUTH TO SOUTHEAST. THIS MAY HELP TO BREAK CAP AND INITIATE CONVECTION. BASED ON TRAJECTORY...IT LOOKS LIKE THE BEST AREA FOR ANY SHOWERS/STORMS WILL BE ACROSS THE EXTREME NORTHEAST...WITH LESS OF A CHANCE WESTWARD. ONCE HEATING IS LOST...SHOULD SEE END TO CLOUDS AND SHOWERS/STORMS. SURFACE PATTERN OVERNIGHT EQUATES TO MORE OF A DRAINAGE FLOW MOST AREAS...SHOULD KEEP LOW CLOUDS AND FOG TO A MINIMUM.

D-L

WARM SECTOR WEATHER FOR ILLINOIS TONIGHT WITH GUSTY SW WINDS...UNSEASONABLY WARM MIN TEMPS (ABOUT 12 DEGREES ABOVE NORMAL MAXES!) AND LITTLE OR NO PCPN. PCPN LIMITED TO AREAS NORTH OF WARM FRONT AND AHEAD OF COLD FRONT. A BKN LINE OF LOW AC OR HIGH SC FROM SW MO TO NW IL TO NEAR GRB COINCIDENT WITH 850/700 MB JET. IF WE GET ANY CONVECTION IN WARM SECTOR THAT/S WHERE IT WILL PROBABLY BE. DON/T THINK WE WILL GET ANY CONVECTION THOUGH...AS THERE IS SOME CAP ON DVN SOUNDING AND AN EVEN LARGER INVERSION BETWEEN 800 AND 700MB ON ACARS (COMMERCIAL AIRCRAFT) SOUNDINGS OVER OHARE (AND AIR IS DRY THERE). SO CURRENT FCST OF CHC POPS IN NW TWDS MORNING LOOKS OKAY AS SFC FRONT GETS CLOSER. REST OF STATE SHOULD BE DRY. WILL RAISE MIN TEMPS A FEW DEGREES AND ADJUST WINDS UP A BIT.

UPDATES THIS MORNING WILL INCLUDE SOME SCT SHOWERS FOR WRN WA...HIGHER POPS ETC. 88D SHOWS INDIVIDUAL SHOWERS MOVING FROM 120 TO 175 DEG AT 25 KNOTS. THE MSTR EXTENDS FROM SE WA...WNW THRU THE CENTRAL CASCADES...AND WWD OVER PGTSND...AND IS GRADUALLY SHIFTING N-BUT THERE IS A LOT OF MSTR S OF HERE STILL SO NOT EXPECTING THE SHOWER THREAT TO DRY UP TOO QUICK. BELOW THE SHOWERS IS A WIDESPREAD STRATUS DECK OVR WRN WA...THAT'S NO SURPRISE. VERY NICE ACARS DATA SHOWS 120/25 STEERING WIND FOR THE SHOWERS AS AIRCRAFT CLIMBED OUT OF SEA AND HEADED SE. THE CENTER OF ROTATION IS DOWN IN THE WILLAMETTE...AS SUGGESTED BY SATELLITE AND 700MB ANALYSES. ISSUED A NOWCAST AT 7AM FOPR SHOWERS NEAR TACOMA...AT 8AM THEY WERE OVER THE EAST SIDE DRIFTING TWDS DOWNTOWN SEA...THEY COULD GET HERE BY 9AM IF THEY DON'T DRY UP. SCT SHOWERS COULD HAPPEN ABT ANYWHERE NOW TIL THE CIRCULATION SHIFTS FURTHER INLAND.

MCFARLAND