Prognostic Meteorological Discussion
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FXUS02 KWBC 231551
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1151 AM EDT SUN APR 23 2017

VALID 12Z WED APR 26 2017 - 12Z SUN APR 30 2017

...LATE SEASON WINTER STORM QUITE POSSIBLE FOR THE CENTRAL ROCKIES
AND HIGH PLAINS THIS COMING WEEKEND...

...HEAVY RAIN AND SEVERE WEATHER PROBABLE FOR THE MIDDLE
MISSISSIPPI VALLEY FRI-SUN...


...OVERVIEW...

THE UPPER PATTERN ACROSS THE LOWER 48 WILL BE DOMINATED BY ONE
POSITIVE HEIGHT ANOMALY SW OF CALIFORNIA IN THE PACIFIC OCEAN AND
ANOTHER OVER SE CANADA/WESTERN ATLANTIC. THAT WILL FORCE TROUGHING
IN BETWEEN, WITH A COUPLE LEAD WAVES DEPARTING THE ROCKIES AND
LIFTING THROUGH THE PLAINS BEFORE MOVING ACROSS THE UPPER MIDWEST
INTO THE GREAT LAKES. A MORE SIGNIFICANT SYSTEM MAY DEVELOP IN THE
FOUR CORNERS AREA THIS COMING WEEKEND. IN ADDITION, A CLOSED LOW
OFF THE MID-ATLANTIC COAST WILL WEAKEN AS IT EXITS INTO THE
NORTHWESTERN ATLANTIC.


...GUIDANCE EVALUATION ...

THOUGH THE MODELS/ENSEMBLES CONTINUE TO SHIFT THE EMPHASIS AMONG
SEVERAL SHORT WAVES EMBEDDED IN THE MEAN FLOW FROM THE CENTRAL
PLAINS NORTHEASTWARD, THE RECENT GFS/ECMWF OFFER GOOD AGREEMENT
OVERALL THROUGH THE END OF THE WEEK WITH THEIR ENSEMBLE MEANS. A
MIDDLE GROUND SOLUTION BETWEEN THE GENERALLY SLOWER/DEEPER
ECMWF/EC-ENS MEAN AND QUICKER/WEAKER GFS/GEFS. THIS APPLIES TO THE
FIRST SYSTEM WED-THU MOVING THROUGH THE GREAT LAKES AND THE
SUBSEQUENT (AND POTENTIALLY MORE IMPACTFUL) SYSTEM NEXT WEEKEND IN
THEE CENTRAL/HIGH PLAINS OR UPPER MIDWEST. THIS HAS ALL THE SIGNS
OF A TYPICAL LATE SEASON WINTER STORM WITH HEAVY SNOW ON THE NW
SIDE OF THE LOW IN MARGINALLY COLD AIR AND HEAVY RAIN TO ITS
EAST/SOUTHEAST WITH SEVERE WEATHER IN THE WARM AIRMASS OVER THE
SOUTHERN PLAINS INTO THE MS VALLEY. MODELS DIVERGE MORE
SIGNIFICANTLY BY NEXT SUNDAY WITH THE TRACK OF THE SFC LOW, SO
OPTED TO SPLIT THE ENSEMBLE DIFFERENCE FOR NOW.


...WEATHER HIGHLIGHTS...

BOUTS OF SHOWERS AND LOCALLY MODEST RAIN WILL CONTINUE TO PLAGUE
THE PACIFIC NORTHWEST THROUGH THE REST OF THE WORK WEEK BEFORE
SOME UPPER RIDGING MOVES IN. SNOW IS EXPECTED ACROSS THE RANGES OF
WA/OR AND FARTHER INLAND ACROSS THE MOUNTAINS OF ID/UT/MT/WY/CO
WHICH COULD BE HEAVY AT HIGHER ELEVATIONS. BY FRI INTO THE
WEEKEND, TREND TOWARD A DEEPER/COLDER SYSTEM IN THE ROCKIES MAY
SUPPORT WIDESPREAD MODERATE TO HEAVY SNOW EVEN EAST OF THE ROCKIES
THROUGH THE FOOTHILLS. THIS MAY EXPAND INTO THE HIGH PLAINS LATER
NEXT WEEKEND AS THE SYSTEM LIFTS TOWARD THE GREAT LAKES.

RAINFALL BECOMES WIDESPREAD ACROSS THE PLAINS TO THE MS VALLEY IN
THE MIDDLE TO LATTER PORTION OF THE WEEK WITH BROAD SW FLOW ALOFT
AND SOUTHERLY FLOW AT LOWER LEVELS. THE STORM PREDICTION CENTER
HAS OUTLINED WED/FRI/SAT AS THE BEST CHANCE OF SEVERE WEATHER (FRI
ESPECIALLY OVER OKLAHOMA). LOCALLY HEAVY RAIN IS POSSIBLE IN THE
MID MS VALLEY TO THE SOUTHERN PLAINS LATE IN THE WEEK INTO NEXT
WEEKEND AS GEFS M-CLIMATE QPF VALUES INCREASE TO THE 99TH
PERCENTILE FROM EASTERN OK AND NORTHEASTERN TEXAS THROUGH MISSOURI
TO CENTRAL/SOUTHERN IL.

MUCH OF THE EASTERN THIRD OF THE CONUS WILL SEE INCREASING
TEMPERATURES LATER THIS WEEK AFTER THE COASTAL LOW DEPARTS AND
BEFORE THE NEXT FRONT SINKS SOUTHWARD. RECORD WARM TEMPERATURES
ARE A DISTINCT POSSIBILITY FROM FRIDAY ONWARD FROM THE LOWER RIO
GRANDE VALLEY OF TEXAS EASTWARD THROUGH THE SOUTHEAST INTO THE
MID-ATLANTIC. BELOW AVERAGE TEMPERATURES WILL REMAIN ANCHORED NEAR
THE UPPER TROUGH AXIS ACROSS THE CENTRAL ROCKIES AND NORTHERN
PLAINS TO THE UPPER MS VALLEY. THE PACIFIC NORTHWEST SHOULD REMAIN
COOLER THAN AVERAGE THROUGH THE WEEK BEFORE A RETURN TOWARD MORE
TYPICAL TEMPERATURES. MUCH OF THE SOUTHWEST (SOUTHERN CA INTO
NV/AZ) SHOULD ESCAPE THE COOLER AND WETTER CONDITIONS TO THE NORTH
AND NORTHEAST.


FRACASSO


$$





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