405
FXUS63 KMPX 172122
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
322 PM CST THU JAN 17 2019
SHORT TERM
(THIS EVENING THROUGH FRIDAY NIGHT)
ISSUED AT 322 PM CST THU JAN 17 2019
THE PIECE OF ENERGY EXPECTED TO BRING SNOW ACROSS SOUTHERN
MINNESOTA FRIDAY HAS REACHED THE WESTERN ROCKIES THIS AFTERNOON.
SNOW WILL BEGIN OVER MONTANA AND THE WESTERN DAKOTAS THIS EVENING,
SPREADING EAST TO SOUTHWESTERN MINNESOTA BY EARLY FRIDAY MORNING
AND ACROSS THE REMAINDER OF SOUTHERN MINNESOTA DURING THE MID
MORNING. THIS BAND WILL BE FRONTOGENESIS DRIVEN AND A DEEP DGZ
LAYER WILL HELP SUSTAIN DECENT RATES FOR MOST OF THE DAY SOUTH OF
THE MN RIVER. THE QUESTION IS, AND ALWAYS SEEMS TO BE, HOW FAR
NORTH THE SNOW WILL GET BEFORE DRY AIR WINS OUT. GLOBAL GUIDANCE
AND EVEN THE ENSEMBLES HAVE SHIFTED NORTH TODAY, WITH ALL BUT THE
NAM SUPPORTING 1 TO 2 INCHES EVEN UP TO THE METRO. THIS IS STILL
AN UNLIKELY SCENARIO GIVEN THE DEGREE OF DRY AIR IN THE BOUNDARY
LAYER. THE GRADIENT WILL ALMOST CERTAINLY BE TIGHTER THAN THOSE
MODELS INDICATE. STILL, CANNOT COMPLETELY IGNORE THE RECENT TREND,
SO DID INCREASE POPS SOME UP TO I-94, WITH A DRY FORECAST
REMAINING NORTH OF THAT CORRIDOR. THE SNOW WILL EXIT TO THE
SOUTHEAST FRIDAY EVENING.
TOTAL ACCUMULATIONS WILL DEPEND ON A NUMBER OF FACTORS AND IS
PARTICULARLY SENSITIVE DUE TO THE UNUSUALLY WIDE RANGE OF
POTENTIAL SNOW RATIOS. GIVEN HOW COLD THE ATMOSPHERE IS AND HOW
DEEP THE DGZ IS, RATIOS OF 15-17:1 SEEM REASONABLE. HOWEVER, IF
THE AREA OF BEST LIFT IS TRANSIENT AND SNOW PRODUCTION BECOMES
LESS EFFICIENT, RATIOS MAY BE LOWER THAN THAT DUE TO SMALLER FLAKE
SIZE. QPF ACROSS THE FAR SOUTH IS IMPRESSIVE AND RANGES FROM
1/3-1/2 INCH. IF THOSE RATIOS DO MATERIALIZE, THEN IT SHOULDN'T BE
MUCH OF AN ISSUE TO GET 5 TO 8 INCHES SOUTHWEST OF THE MN RIVER.
CONVERSELY, IF RATIOS ARE MORE 12:1 OR SO, THEN WE MAY BE TALKING
CLOSER TO 3 TO 7 INCHES. UPGRADED PARTS OF THE ADVISORY TO A
WINTER STORM WARNING FOLLOWING COLLABORATIVE EFFORTS WITH WPC AND
THE SURROUNDING OFFICES AND EXPECTED THE ADVISORY SLIGHTLY
NORTHWARD AS WELL.
LONG TERM
(SATURDAY THROUGH THURSDAY)
ISSUED AT 322 PM CST THU JAN 17 2019
OVERALL, THE LONG TERM PERIOD STILL LOOKS TO BE COOLER THAN
NORMAL WITH WIDESPREAD LIGHT SNOW LOOKING LIKELY FOR NEXT WEEK.
BY SATURDAY, WE'LL BE IN THE WAKE OF THE DEPARTING SYSTEM WITH
NORTHERLY FLOW AND TEMPERATURES A SOLID 10 TO 20 DEGREES BELOW
NORMAL. THE MORNING WILL START OUT COLD, WITH TEMPS BELOW ZERO IN
WESTERN AND CENTRAL MN, AND WIND CHILLS HOVERING NEAR THE -25
DEGREE MARK TO START THE DAY ACROSS MUCH OF WESTERN MN.
BY LATE SATURDAY NIGHT, AN APPROACHING 850MB TROUGH WITH DECENT
THETA-E ADVECTION AND ISENTROPIC LIFT ALONG WITH AN UPPER LEVEL
VORT MAX WILL SLIDE SOUTHEAST ACROSS MUCH OF WESTERN/SOUTHWESTERN
MN AND BRING ABOUT AN INCH OR SO OF SNOW TO THAT AREA.
THEN ATTENTION TURNS TO A POSITIVELY TILTED UPPER TROUGH THAT
WILL DIG ACROSS THE WESTERN CONUS ON MONDAY. A SURFACE CYCLONE
WILL EMERGE ACROSS CO AND TRANSLATE EASTWARD THROUGH TUESDAY. AN
INVERTED TROUGH EXTENDING NORTHWARD INTO MN WILL BE SUPPORTED BY
UPPER LEVEL VORTICITY ADVECTION AND DECENT DIFFERENTIAL DIVERGENCE
THANKS TO THE LEFT EXIT REGION OF A STRENGTHENING JET MOVING
THROUGH THE REGION. THIS STILL LOOKS LIKE A LIGHT SNOW EVENT
ACROSS A BROAD AREA.
DEEP NORTHWEST FLOW LOOKS TO FOLLOW INTO MIDDLE OF NEXT WEEK WITH
BELOW NORMAL TEMPERATURES AND THE OPPORTUNITY FOR A QUICK-MOVING
CLIPPER SYSTEM TO MOVE THROUGH LATE NEXT WEEK.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1256 PM CST THU JAN 17 2019
MVFR CONTINUES ACROSS WI EARLY THIS AFTERNOON, AND HAS MOVED BACK
INTO THE KAXN AREA. OTHERWISE, PARTLY CLOUDY SKIES BETWEEN THESE
AREAS. VFR CONDITIONS WILL RETURN AREA WIDE LATER TODAY OR THIS
EVENING BEFORE SNOW ADVANCES EASTWARD ACROSS SOUTHERN MN FRIDAY
MORNING WITH IFR CONDITIONS.
KMSP...VFR THROUGH THE PERIOD IS LIKELY. IT REMAINS TO BE SEEN
WHETHER THE SNOW WILL REACH MSP FRIDAY, THE NORTHERN EDGE WILL BE
CLOSE. MVFR CONDITIONS WOULD ACCOMPANY THE SNOW WITH THE STEADIEST
LIKELY REMAINING SOUTH.
/OUTLOOK FOR KMSP/
FRI NIGHT...VFR. WIND NE 7 KTS.
SAT...VFR. WIND NNW 15G25 KTS.
SUN...MVFR PSBL. WIND LIGHT & VRBL.
MPX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...WINTER STORM WARNING FROM 6 AM TO 10 PM CST FRIDAY FOR MNZ074-
082-083-091>093.
WINTER WEATHER ADVISORY FROM 6 AM TO 10 PM CST FRIDAY FOR MNZ067-
075>077-084-085.
WINTER WEATHER ADVISORY FROM 4 AM TO 6 PM CST FRIDAY FOR MNZ054-
056-064-065-073.
SHORT TERM...BORGHOFF
LONG TERM...SPD
AVIATION...BORGHOFF
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