Forecast Discussions mentioning ACARS, received at FSL on 04/16/01

WINTER RETURNS...A DEEP SHORTWAVE TROF WILL BE OVER THE REGION TUE THRU THU WITH WEAK RIDGING FOR FRIDAY. THIS FEATURE HAS BEEN FORECASTED TO OCCUR FOR A WEEK AND WHILE IT WILL NOT BE A DEEP AS ORIGINALLY FCSTED...IT'S STILL A 2 SIGMA ANOMALY AND 1000-500 MB THICKNESS OF 520 DM ARE IMPRESSIVE TO MID TO LATE APRIL.

SHORT TERM...PCPN OVER REGION IS LIGHT WITH GOOD BRIGHT BANDING SEEN ON RADAR. PIREP FROM GON-TTN AT 05Z REPORTED SNOW AT 040. WET BULB ZERO IS AT AROUND 3K AND ACARS SOUNDINGS SHOWING FREEZING LEVEL AROUND 4K. 999 MB LOW LOCATED EAST OF NORFOLK AS OF 06Z.

SUNY MM5 DISCUSSION... ETA AND MM5 12KM BOTH SLOW ON GETTING TO THE 06Z SFC LOW POSITION. ETA DOES A BETTER JOB IN CATCHING UP THAN THE MM5 DOES. THE MM5 DEVELOPS A DOUBLE LOW STRUCTURE WHICH TAKES UNTIL LATE THIS AFTERNOON TO GET ABSORBED INTO A SINGLE LOW CENTER. THE 36 KM HAS HINT OF THIS TOO WHICH MAKES ME THINK IT IS NOT AN ARTIFACT OF THE HIGHER RESOLUTION BUT SOME MODEL ARTIFACT? INTERESTINGLY...THE PSU 25 KM MM5 00Z RUN DOES NOT SHOW THIS DOUBLE LOW STRUCTURE.

AVN...ETA AND MM5 ALL HAVE A 996 CENTER AT 18Z 300+ MILES SE OF MONTAUK.

PCPN OVER WESTERN PORTION WILL END VERY EARLY THIS AM WITH NOTHING MEASURABLE AFTER 12Z (I HOPE) AS SUPPORT ERODES AND LOW DISCUSSED ABOVE BECOME PRIMARY FEATURE. EXPECT BREAKS OF SUN THIS AFTERNOON IF NOT BETTER.

SHORTWAVE DROPS IN FROM THE GREAT LAKES LATE TONIGHT. MM5 AND ETA ROTATE A BAND OF PCPN ACROSS THE REGION TUE MORNING WITH THE HEAVIER PCPN TO THE NORTH OF THE CITY AND LI. ETA AND 12KM MM5 PRODUCES SOME CONVECTIVE PCPN WHICH IS WHAT I'D EXPECT WITH THE INSTABILITY. WILL NOT TRY TO TIME THIS EVENT YET FOR TUESDAY FOR INSTABILITY COULD BE HIGHER IN THE PM AS SUN COMES OUT.

DISCUSSED QPF WITH ALY AND FEELING HERE IS THAT QPF HERE LESS THAN 1/4 INCH. MODELS FOCUS QPF IN THEIR AREA ACCORDINGLY. MM5 4KM RUN SHOW SOME MESOSCALE STRUCTURE TO THE PCPN OVERNIGHT.

PCPN TYPE...HAVE TO USE THE ETA SOUNDINGS AS ANY THICKNESS TECHNIQUES PRODUCE A LOT OF SNOW. THINKING IS THAT ETA SOUNDINGS ARE TYPICALLY TOO WARM. WILL INCLUDE POSSIBLY MIXED FOR THE HIGHT ELEVATIONS INLAND.

SHOWERY WX CONTINUES ON WED.

NEXT PCPN EVENT APPEARS TO BE LATE FRIDAY AS A WARM FRONT.

MARINE...SEAS GET TO SCA ON TUE. OTHERWISE NO PROBLEMS.

EQUIPMENT...RADAR HAVING SOME CALIBRATION PROBLEMS. WILL HAVE TECHNICIANS INVESTIGATE IN THE AM. DO NOT TRUST ANY OKX PCPN ESTIMATES.

HYDRO: CT RIVER IN FLOOD...REFER TO BOSFLSBOS FOR MORE INFO.

.OKX... CT...FLW FOR CT RVR CTZ007 (VIA WFO BOX). NJ...NONE NY...NONE MARINE...NONE.

$$

TONGUE



.OVERVIEW... A HIGH AMPLITUDE PATTERN CONTINUES ACROSS THE PACIFIC AND NORTH AMERICA WITH RIDGING ALONG 170W...A DEEP TROUGH ALONG 140W...AND AN OMEGA BLOCK ALONG 110W. MODEL PERFORMANCE ON THE LARGE SCALE HAS BEEN QUITE GOOD...BUT AS SUSPECTED FOR THE PAST FEW DAYS SMALL DIFFERENCES IN THE POSITION OF THE FRONT ASSOCIATED WITH THE OFFSHORE TROUGH IS CAUSING SHORT TERM FORECAST HEADACHES IN WESTERN WASHINGTON. THE 00Z MODELS --AVN/MESOETA/MM5-- APPEAR REASONABLE WELL INITIALIZED OFFSHORE. BUT ACARS DATA SEEM TO INDICATE SOME PLACEMENT PROBLEMS WITH INDIVIDUAL JET STREAKS ROTATING AROUND THE OFFSHORE VERTICALLY STACKED LOW NEAR 41N/140W. SPECIFICALLY THE FIRST JET STREAK TO THE SE OF THE LOW THAT IS NOW PULLING NNE APPEARS TO BE INITIALIZED TOO STRONG. THE NEXT JET STREAK AND SHORT WAVE ROTATING AROUND THE SW PART OF THE LOW APPEARS TO BE WELL PLACED PER WATER VAPOR IMAGERY...AND IT IS THIS SHORT WAVE THAT BRINGS THE PRECIPITATION SHIELD WITH THE OFFSHORE FRONT INLAND THIS EVENING. WILL USE A COMBINATION OF SATELLITE IMAGERY...AND MESOSCALE MODELS IN THE FIRST PERIOD...THEN TREND TOWARD THE AVN IN FOR THE SECOND PERIOD THROUGH WEDNESDAY. SUSPECT THAT NO MODEL WILL NAIL DOWN THE TIMING OR STRENGTH OF INDIVIDUAL FEATURES MOVING THROUGH A NEARBY LONG WAVE TROUGH IN THE EXTENDED...SO WILL CONTINUE TO USE A BROAD BRUSH THERE.

.SHORT TERM... LIGHT PRECIPITATION WILL FLIRT WITH THE COAST AND OLYMPICS TODAY...BUT WILL STAY OUT OF THE INTERIOR UNTIL LATE AFTERNOON AT BEST GIVEN OFFSHORE PRESSURE GRADIENTS AND SLY FLOW ALOFT. ALL SHORT TERM GUIDANCE KEEPS PCPN W OF A KCLM-KSHN-KSPB LINE UNTIL RIGHT AFTER 00Z WHEN A SURGE OF SLY GRADIENTS MOVES NWD WITH THE PASSING SHORT WAVE. GIVEN THIS SCENARIO...NOT UNCOMMON FOR THE SPRING...WILL LOWER POPS TODAY AND RAISE TEMPERATURES INTO THE LOWER TO MID 60S IN THE INTERIOR. THEN HIGH POPS AND COOLING TAKES PLACE TONIGHT AND TUE AS THE FRONTAL BAND MOVES SLOWLY EWD. DESPITE WARM TEMPERATURES THIS AFTN...INSTABILITY IN ALL MODELS NOW INSUFFICIENT TO PROVIDE A CONVECTIVE THREAT.

.EXTENDED...CURRENT EXTENDED FORECASTS LOOK GOOD PER ABOVE DISCUSSION.

UIL 8++ SEA 388 OLM 499 ALBRECHT

.SEW...SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA.

.KATX...VCP31/CSR31...OPERATIONAL