Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3
000
FXUS02 KWBC 250607
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 AM EDT TUE APR 25 2017

VALID 12Z FRI APR 28 2017 - 12Z TUE MAY 02 2017

...LATE SEASON WINTER STORM LIKELY FOR THE FRONT RANGE OF WY/CO
AND POSSIBLE FOR THE HIGH PLAINS THIS COMING WEEKEND...

...HEAVY RAIN PROBABLE FOR THE MIDDLE TO LOWER MISSISSIPPI VALLEY
OVER THE WEEKEND...

...OVERVIEW AND GUIDANCE EVALUATION...

THE UPPER PATTERN ACROSS THE LOWER 48 WILL BE DOMINATED BY A
PERSISTENT TROUGH EXTENDING FROM THE SOUTHERN ROCKIES ACROSS THE
CENTRAL PLAINS AND MS VALLEY AND UPPER GREAT LAKES. THE TROUGH IS
FLANKED ON BOTH SIDES IN THE EASTERN PACIFIC AND WESTERN
ATLANTIC/EAST COAST WITH HIGH AMPLITUDE RIDGES.

WITHIN THE CENTRAL US TROUGH...A PERSISTENT FRONTAL BNDRY EXTENDS
FROM THE SOUTHERN PLAINS  TO THE UPPER GREAT LAKES.  THE MODELS
SHOW ONE WAVE OF LOW PRESSURE ALONG THE FRONT 12Z FRI IN EASTERN
KS THAT MOVES UP THE BNDRY AND DISSIPATES.  A DEEPER AND MORE
PERSISTENT CYCLONE DEVELOPS BY SAT MORNING 29 APR IN THE RED RIVER
VALLEY AND NORTH TEXAS AND MOVES NORTHEAST ACROSS THE SOUTHERN
PLAINS TO THE MID MS VALLEY SUN 30 APR AND THEN EITHER THE GREAT
LAKES OR UPPER MS VALLEY MON BEFORE EXITING INTO CANADA.

THE 18Z GFS AND 12Z ECMWF WERE IN CLOSE AGREEMENT WITH ONE
ANOTHER, BUT THE 00Z GFS REVERTED TO A MORE WESTERN LOW TRACK IN
THE UPPER MS VALLEY OVER THE WEEKEND. THE PRIMARY DIFFERENCES
AMONG THE MODELS AND ENSEMBLE MEANS WAS THE 12Z ECMWF ENSEMBLE
MEAN AND 18Z GEFS MEAN WERE SEVERAL HOURS SLOWER THAN THE
OPERATIONAL RUNS IN MOVING THIS CYCLONE ACROSS THE LAKES OR UPPER
MS VALLEY INTO CANADA.
THE PREFERENCES OVERALL FOR DAYS 3-7 WERE TO BLEND THE OPERATIONAL
ECMWF/18Z GFS WITH THE RESPECTIVE ECMWF/GEFS ENSEMBLE MEANS.

A SYSTEM MOVING ONSHORE IN BRITISH COLUMBIA ON SUN THEN MOVES
SOUTHEAST AND CROSSES INTO THE NORTHERN PLAINS MON AND THEN INTO
THE UPPER MS VALLEY TUE 02 MAY...WITH BETTER THAN AVERAGE
AGREEMENT AMONG THE GFS/ECMWF/ENSEMBLE MEANS...SO AGAIN A FOUR WAY
AVERAGE/CONSENSUS WAS USED FOR THE FORECAST.


...WEATHER HIGHLIGHTS...

SNOW IS EXPECTED ACROSS THE RANGES OF ID/UT/MT/WY/CO. BY FRI INTO
THE WEEKEND, THE ECMWF AND GFS BOTH SHOW WIDESPREAD MODERATE TO
HEAVY SNOW FROM THE WY/CO FRONT RANGE INTO THE FOOTHILLS. THE SNOW
MAY EXPAND INTO THE HIGH PLAINS ON SAT   AS COLD AIR IS ADVECTED
SOUTH DOWN THE PLAINS ON THE WESTERN SIDE OF THE CIRCULATION.  THE
00Z GFS AND 12Z ECMWF ALSO SHOW POTENTIAL FOR SNOW ON THE
NORTHWEST FRINGE OF THE PRECIP SHIELD IN THE UPPER MS VALLEY AND
AREAS AROUND LK SUPERIOR...BUT THE ENSEMBLE MEANS ARE MUCH LIGHTER
RIGHT NOW.

RAINFALL BECOMES WIDESPREAD ACROSS THE CENTRAL PLAINS THU AND THU
NIGHT WITH A SHOT OF WARM ADVECTION AND AGAIN FRI AS THE SOUTHERN
PLAINS STORM DEVELOPS AND MOISTURE SURGES NORTH...CONTINUING INTO
THE MID MS VALLEY AND GREAT LAKES OVER THE WEEKEND. SEE THE STORM
PREDICTION CENTER CONVECTIVE OUTLOOKS THAT ADDRESS SEVERE WEATHER
POTENTIAL. LOCALLY HEAVY RAIN IS POSSIBLE IN THE MID TO LOWER MS
VALLEY TO THE SOUTHERN PLAINS THIS WEEKEND AS GEFS M-CLIMATE QPF
VALUES INCREASE TO THE 97 TO 99TH PERCENTILE FROM EASTERN OK AND
NORTHEASTERN TEXAS THROUGH MISSOURI TO CENTRAL/SOUTHERN IL. BOTH
THE OPERATIONAL ECMWF/GFS SHOW POTENTIAL FOR SEVERAL INCHES OF
RAIN FROM MO TO SOUTHEAST OK/NORTHEAST TEXAS AND ACROSS AR AND
ADJACENT PARTS OF LA AND MS.

MUCH OF THE EASTERN THIRD OF THE CONUS WILL SEE WELL ABOVE NORMAL
TEMPERATURES DAYS 3-6 BEFORE MODERATING TOWARDS NORMAL WITH A
FRONTAL PASSAGE DAY 7 TUE 02 MAY. AREAS OF RECORD WARM
TEMPERATURES ARE EXPECTED FROM FRIDAY 28 APR THROUGH SUNDAY 30 APR
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 PLAINS TO THE UPPER MS VALLEY AND UPPER GREAT LAKES.
MUCH OF THE SOUTHWEST (SOUTHERN CA INTO NV/AZ) SHOULD TREND TO
ABOVE NORMAL TEMPERATURES AT THE END OF THE WEEKEND INTO EARLY
NEXT WEEK.

PETERSEN


$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.