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Prognostic Meteorological Discussion
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000
FXUS02 KWBC 270640
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
239 AM EDT FRI APR 27 2018

VALID 12Z MON APR 30 2018 - 12Z FRI MAY 04 2018

...OVERVIEW...

ON MONDAY...A BROAD CYCLONIC CIRCULATION WILL BE IN THE PROCESS OF
EXITING THE NORTHEASTERN U.S. WHILE AMPLIFIED FLOW LOOMS UPSTREAM
OVER THE REMAINDER OF THE COUNTRY. MEAN UPPER RIDGING SHOULD
CONTINUE ADVANCING FROM THE MS RIVER VALLEY TOWARD THE EASTERN
SEABOARD DURING THE MONDAY-THURSDAY TIMEFRAME AS HEIGHTS LOWER
OVER THE WESTERN/CENTRAL STATES. WITHIN THIS REGION OF
TROUGHING...TWO SEPARATE SYSTEMS ARE FORECAST TO EJECT TOWARD THE
CENTRAL U.S. DURING THE PERIOD. INITIALLY...A SHORTWAVE SHOULD
LIFT TOWARD THE NORTH-CENTRAL STATES WITH THE POTENTIAL FOR A DEEP
SURFACE LOW TO CROSS THE DAKOTAS ON TUESDAY MORNING BEFORE LIFTING
INTO ONTARIO BY MID-WEEK. THE PARENT UPPER TROUGH SHOULD RE-LOAD
AS HEIGHTS LOWER ACROSS THE SOUTHWESTERN U.S. WITH AN EVENTUAL
EASTWARD PROGRESSION OF THIS MEAN TROUGH. THIS WILL ULTIMATELY
USHER A COLD FRONT ACROSS THE MS RIVER VALLEY BY DAY 7/MAY 4.


...MODEL EVALUATION/UNCERTAINTIES/PREFERENCES...

THE DEPARTING UPPER LOW OVER THE NORTHEASTERN STATES IS WELL
RESOLVED WITH SOME UNCERTAINTIES REGARDING TIMING...PARTICULARLY
AS THE 00Z GUIDANCE HAS COME IN SLOWER. HOWEVER...THE 12Z ECMWF
STILL SITS ON THE WESTERN SIDE OF THE SPREAD ON TUESDAY AS
SUGGESTED BY THE ENSEMBLE SPAGHETTI PLOTS. CONSIDERING THE
EVOLVING WESTERN/CENTRAL U.S. TROUGH...MODELS STILL ARE UNCERTAIN
REGARDING THE INTENSITY OF THE CYCLONE LIFTING TOWARD THE
DAKOTAS/UPPER MIDWEST ON TUESDAY. THE PAST SEVERAL RUNS OF THE GFS
HAVE BEEN MORE EMPHATIC WITH THE DEEPER SOLUTION WHILE THE CMC
SOLUTION CONTINUES TO BOUNCE AROUND A BIT. MEANWHILE...THE 12Z/00Z
ECMWF RUNS ARE DECIDEDLY WEAKER AS DICTATED BY THE FLATTER
MID-LEVEL SHORTWAVE. SHIFTING FOCUS BACK TO THE SECONDARY HEIGHT
FALLS...IT REMAINS WELL AGREED UPON OUTSIDE OF THE 12Z UKMET WHICH
SHIFTED THE ENTIRE TROUGH DOWNSTREAM. FORTUNATELY...THE LATEST
UKMET HAS MADE A WESTWARD ADJUSTMENT BRINGING ITS SOLUTION CLOSER
TO THE UPSTREAM CONSENSUS. THE ENTIRE SYNOPTIC PATTERN SHOULD
ULTIMATELY SHIFT EASTWARD ALLOWING THIS SYSTEM TO CROSS THE
VICINITY OF THE MS RIVER VALLEY BY LATE NEXT WEEK. BY DAY 7/MAY
4...A MEAN RIDGE SHOULD SETTLE OVER THE WEST COAST WITH THE
POTENTIAL FOR A WEAKNESS ACROSS THE FOUR CORNERS REGION. ENSEMBLE
MEAN SOLUTIONS ARE WELL CLUSTERED AND SUPPORTIVE OF THIS ULTIMATE
SET UP.

THROUGH MID-WEEK...FAVORED A COMBINATION OF THE 18Z/12Z GFS WITH
THE 12Z ECMWF/CMC GIVEN DECENT MODEL AGREEMENT. INCLUSION OF THE
12Z ECMWF DID INCREASE PRESSURES A BIT WITH THE NORTH-CENTRAL U.S.
CYCLONE. GRADUALLY INCORPORATED THE 18Z GEFS/12Z ECMWF ENSEMBLE
MEANS INTO THE MIX THROUGH THE REMAINDER OF THE PERIOD GIVEN
GROWING UNCERTAINTIES. WAS ABLE TO MAINTAIN AT LEAST 30 PERCENT OF
AN OPERATIONAL COMPONENT IN THE BLEND THROUGH LATE NEXT WEEK GIVEN
A DECENT HANDLE ON THE OVERALL PATTERN.


...THREATS/WEATHER HIGHLIGHTS...

UNDERNEATH THE UPPER LOW ACROSS NEW ENGLAND...CHILLY TEMPERATURES
ACCOMPANIED BY WRAP AROUND RAIN SHOWERS WILL BE LIKELY EARLY NEXT
WEEK. FARTHER UPSTREAM...MULTIPLE ROUNDS OF SHOWERS AND
THUNDERSTORMS ARE EXPECTED IN ADVANCE OF THE SLOW MOVING UPPER
TROUGH. THE INITIAL THREAT AREA WILL EXIST OVER THE NORTHERN
ROCKIES/GREAT PLAINS AND INTO THE UPPER MIDWEST THROUGH MID-WEEK
WITH A SOUTHERN SHIFT EXPECTED AS THE TROUGH RELOADS OVER THE
WEST. AN ELONGATED AXIS OF MODERATE TO HEAVY RAINFALL WILL LIKELY
EXTEND FROM THE SOUTHERN PLAINS UP TOWARD THE GREAT LAKES AS THE
COLD FRONT EDGES EASTWARD. SOME AREAS OF SEVERE WEATHER MAY BE
POSSIBLE AS SUGGESTED IN THE PREVIOUS STORM PREDICTION CENTER
OUTLOOK. THERE COULD ALSO BE SOME THREAT FOR RATHER IMPRESSIVE
RAINFALL AMOUNTS AS SHOWN BY SOME OF THE MORE RELIABLE OPERATIONAL
GUIDANCE. THIS WOULD PARTICULARLY BE THE CASE OVER THE ARKLATEX
INTO THE OZARKS.

WITH A PROGRESSIVE PATTERN IN PLACE...EXPECT RELATED TEMPERATURE
ANOMALIES TO NUDGE DOWNSTREAM IN TIME. AS MENTIONED...COOLER
TEMPERATURES WILL INITIALLY PREVAIL OVER THE EASTERN U.S. WHILE
WELL ABOVE AVERAGE READINGS OCCUPY THE CENTER OF THE COUNTRY. SUCH
DEPARTURES ON THE ORDER OF 10 TO 15 DEGREES ABOVE CLIMATOLOGY WILL
ADVANCE EASTWARD IN TIME WITH LOW TO POSSIBLY MID 80S LIKELY TO
REACH THE CENTRAL APPALACHIANS AND MID-ATLANTIC ON
WEDNESDAY/THURSDAY. THE COOLEST CONDITIONS SHOULD GENERALLY BE
FOUND UNDERNEATH THE EXTENSIVE PRECIPITATION SHIELD AND IN THE
WAKE OF THE UPPER TROUGH GIVEN A COLD ADVECTION PATTERN. EXPECTED
TEMPERATURES SHOULD BE AROUND 5 TO 10 DEGREES BELOW AVERAGE IN
SUCH LOCATIONS.



RUBIN-OSTER


ASSOCIATED WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS...SURFACE
SYSTEMS...WEATHER GRIDS...QUANTITATIVE PRECIPITATION FORECASTS
(QPF)...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITIES CAN BE
FOUND AT...

http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4


$$
National Weather Service National Headquarters
