February Action?

Major Winter Storm Febraury 8th -12th Thoughts:

There continues to be a lot of uncertainty regarding the upcoming weekend and early next week as a long wave trough develops across the West. What we do know is a deep trough with a Potent Winter Storm will develop across the Great Basin and Intermountain West. In fact the HPC has so little confidence in the guidance, they have tasked a NOAA G-IV Winter RECON mission to fly the Pacific and sample the environment. Across the W, wintry conditions appear likely beginning Thursday as a potent storm system moves inland along the Pacific NW/British Columbia area and drop SSE and closes off near the California/Arizona/Mexico border with temps aloft expect to drop to the -30+ range as the cold core 500mb upper low forms. Due to lack of guidance continuity, the implications of how that storm ejects from the Great Basin is the main concern for the late weekend/early next week time frame. The HPC is mentioning this morning the similarity to a Spring like storm we tend to see in late March/early April meaning a wide spread severe weather event in the warm sector that extends from Eastern New Mexico/Texas/Oklahoma and portions of Kansas with wintry weather in the cold sector N of the Polar jet. The fly in the ointment is will there be phasing with yet another short wave riding the Polar jet across Southern Canada into the Northern Plains with the active southern jet stream storm which would tend to pull down cold air from the N and collide with warm moist Gulf air to the S. The Sub tropical jet appears to come into play as well as tropical forcing increasing across the Eastern Pacific energizing the Great Basis storm We are in a somewhat zonal split flow pattern where cold air has retreated N with an active northern stream and a secondary active southern stream where this storm system will organize later this week. All in all a very active pattern is ahead and for much of the CONUS as rain chances are returning this week to the Gulf Coastal Regions with an active southern stream and the Pacific NW as the Gulf of Alaska storm moves inland. The finer details regarding the Medium Range forecast should become bit clearer later in the week as data from WSR scheduled to begin 06/0000 regarding next weekend into early next week and the sensible weather we can expect.

EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

142 AM EST MON FEB 04 2013

VALID 12Z THU FEB 07 2013 - 12Z MON FEB 11 2013

DAYS 3-5...

OVERNIGHT SURFACE GRAPHICS WERE ABLE TO MAINTAIN VERY GOOD

CONTINUITY WITH A BLEND OF THE 3/12Z ECMWF AND ITS ENSEMBLE

MEANS...ALONG WITH SOME OF THE 3/12Z UKMET. THE 4/00Z GFS GETS TO

BE A FAST OUTLIER BY FRIDAY (DAY 4) WITH THE 'CLIPPER' RACING

THROUGH THE OHIO VALLEY AND OFFSHORE INTO THE WESTERN ATLANTIC.

THE 4/00Z UKMET-ECMWF WERE BETTER FITS TO THE MANUAL GRAPHICS AND

THE PATTERN EVOLVING VS THE 4/00Z GFS-CANADIAN.

WITH MUCH OF THE 4/00Z GUIDANCE IN...THERE IS PLENTY OF SUPPORT

FOR COMPLEX COASTAL WAVE DEVELOPMENT AND SECONDARY INTENSIFICATION

OF A SURFACE WAVE OFF THE IMMEDIATE COASTLINE (IN THE OUTER BANKS

AND BLOCK ISLAND CORRIDOR) ON FRIDAY AFTERNOON/EVENING. THE MANUAL

GRAPHICS CERTAINLY ARE NOT PERFECT PROGS...BUT I DID DRAW A SFC

LOW TRACK (AND INTERMEDIATE POSITION)...PASSING OVER THE BENCHMARK

BEFORE 9/00Z IN THE NEIGHBORHOOD OF 1004 MB AND DEEPENING TO 996MB

EAST OF HALIFAX NS AROUND 9/12Z. THIS INTERMEDIATE PROG (VALID

9/00Z) IS CLOSER TO THE 4/00Z UKMET FOR DEPTH BUT HONORS THE TRACK

OF THE 3/12Z ECMWF PACKAGE AND THE 4/00Z OPERATIONAL ECMWF. THE

DEEPEST SFC PRESSURE AT 983 MB AS IT ENTERS THE SW GULF OF MAINE

AFTER 9/00Z MIGHT BE OVERDONE...BUT THE TRENDS FROM YESTERDAY

SUPPORT ONE LAST CYCLONE (CLIPPER) BEFORE THE ARCTIC AIRMASS

RETREATS AWAY FROM THE EASTERN SEABOARD.

DAYS 6-7...

THE MEDIUM RANGE GUIDANCE HAD A GOOD HANDLE ON THE WEST COAST

TROUGH AND MODERATELY-INTENSE CYCLONE EXITING THE SOUTH CENTRAL

ROCKIES NEXT WEEKEND. AS ENVISIONED A COUPLE OF DAYS AGO...THE

SYSTEM HAS SLOWED A TAD...BUT WILL SWEEP SOME PACIFIC ENERGY AND A

WEAK SURFACE REFLECTION ACROSS THE NORTHERN ROCKIES AND THROUGH

THE NORTH DAKOTA PLAINS BEFORE THIS NORTHERN END OF THE FRONT

WEAKENS IN NORTHERN MINNESOTA AND WESTERN ONTARIO.

THE MANUAL H5 TRACK FOR THIS SYSTEM DOWNSTREAM OF THE FRONT RANGE

WAS DRAWN WITH A 'BEST FIT' LINE FROM PUEBLO CO TO MINNEAPOLIS MN

GIVEN THE VARIABILITY IN TRACK AND SPEED. THE GFS IS THE MAIN

REASON THERE IS 'INTRODUCED UNCERTAINTY'. I CAN NOT REALLY FOLLOW

ITS RUN TO RUN ADJUSTMENTS...BUT THE H5 TRACK IS NOT FAR FROM THE

TRACK ENVISIONED FOR NEXT WEEKEND. THE WESTERN GOMEX SHOULD BE

WIDE OPEN AHEAD OF THIS CYCLONE.

THE ONE TREND THAT WILL NEED TO BEAR WATCHING...IS...HOW THE

INTENSE WEST-NORTHWESTERLY FLOW SURGING THROUGH THE 4 CORNERS AND

SOUTHERN DIVIDE REGION ON SATURDAY TRANSLATES DOWNSTREAM OVER THE

SOUTHERN HIGH PLAINS OF ERN NM/WRN TX LATER ON SATURDAY AFTERNOON

AND EVENING. IN SOME RESPECTS...THIS PACIFIC SYSTEM LOOKS MORE

LIKE A LATE MARCH/EARLY APRIL SYSTEM... WITH A WELL-DEFINED DRY

SLOT AND WARM ADVECTION WORKING NNEWD ACROSS THE TX PANHANDLE AND

SOUTH CENTRAL KANSAS...AND INTO THE H5 CYCLONE'S CIRCULATION. THIS

MAY END UP SHIFTING THE GULF MOISTURE EAST AND SOUTH OF THE COLD

FRONT INITIALLY...AND BRIEFLY LIMIT THE PHASING OF THE LOW-LEVEL

MOISTURE LIFTING ATOP THE COLD SECTOR OF THIS SYSTEM INVOF 40N

LATITUDE AND BETWEEN 94W-99W LONGITUDE. LIKEWISE..A DRIER EASTERLY

LOW-LEVEL FLOW IS ANTICIPATED TO BE WORKING INTO THIS SYSTEM ALONG

ITS NORTHERN PERIPHERY THROUGH EARLY SUNDAY.

VOJTESAK

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