FXUS63 KDLH 022118
AFDDLH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DULUTH MN
318 PM CST WED DEC 2 2009
.DISCUSSION...
DISCUSSION...FOCUS WILL BE ON LAKE EFFECT SNOW TONIGHT THROUGH THE
DAY THURSDAY.
GETTING TO THE LAKE EFFECT SNOW FIRST..WE CURRENTLY ARE CONTINUING THE
LAKE EFFECT SNOW ADVISORY...BUT HAVE EXTENDED IT TO CONTINUE THROUGH
ABOUT 10 PM ON THURSDAY. A NICE BAND OF LAKE EFFECT BAND CLOUDS
HAS SETUP TODAY...THOUGH NOT MUCH WAS GOING ON YET TODAY UNTIL THE
PAST 15-30 MINS. WEB CAMS IN HURLEY HAVE INDICATED SNOW HAS BEGUN
TO FALL...IRONWOOD IS DOWN TO 3SM VSBY WITH -SN. WE ARE STILL
LOOKING AT THE GENERAL IDEA OF 4-7 INCHES OVER A 24 HOUR PERIOD.
LATEST QPF FROM THE 12Z NAM BRINGS ABOUT 0.3-0.4" OF LIQUID
EQUIVALENT PRECIP TO THE WI SNOWBELT...AND THE GFS IS AROUND 0.3".
THE PREVIOUS FEW RUNS HAD BEEN BACKING OFF ON QPF A BIT...BUT THE
12Z RUNS HAVE RAMPED BACK UP A TOUCH...AND GENERALLY HAVE BEEN
FAIRLY CONSISTENT AROUND THE 0.3" MARK.
THE GENERAL PROGRESSION OF THE SNOWFALL WILL BEGIN WITH WINDS
BECOMING NNE PRODUCING A VERY NICE FETCH ACROSS WESTERN LAKE
SUPERIOR FOR SUFFICIENT LATENT HEAT FLUX INTO THE BOUNDARY LAYER. 850
TEMPS IN THE -10 TO -12 C RANGE COUPLED WITH LAKE TEMPS OF 6C OR SO
GIVE COLLIER INDEX VALUES IN THE CONDITIONAL/BORDERLINE MODERATE
CATEGORY. EXPECT THE BEST ACCUMULATION OVERNIGHT. WINDS ON THURSDAY
THEN BACK AND BECOME MORE NW WHICH REDUCES THE FETCH..BUT BY THIS
TIME THINGS HAVE GOTTEN GOING...AND 850 TEMPS DECREASE TO TO -12 TO
-13C CREATES COLLIER INDEX VALUES IN THE MODERATE RANGE LATE TONIGHT INTO
THURSDAY. COLDER TEMPS WILL THEREFORE PROMOTE HIGHER SNOW TO LIQUID
RATIOS DURING THE MORNING THURSDAY GETTING INTO THE 15-20:1 RANGE...SO
SIMILAR ACCUMULATIONS CAN BE EXPECTED DURING THE MORNING THOUGH
MAYBE LIGHTER QPF. WINDS THEN BACK THURSDAY AFTERNOON EVEN MORE
PUSHING BEST CHANCES INTO IRON COUNTY AND FURTHER EAST.
ADDITIONALLY WITH REGARDS TO THERMODYNAMICS AND MOISTURE...LAKE
INDUCED CAPE VALUES ARE IN THE 300-450 J/KG RANGE...WHICH ARE DOWN A
BIT FROM EARLIER IN THE WEEK VALUES BUT STILL NOT TOO BAD. INVERSION
HEIGHTS ARE ALSO MODERATE PER BUFR SOUNDINGS FOR KIWD...IN THE 7000
FT RANGE. AND WHILE THE LOW LEVELS ARE PLENTY SATURATED WITH ALL THE
LIFT IN THE LOWEST 6-7K FT...DEEPER LAYER SATURATION IN THE
850-700 LAYER HOVERS IN THE 60-70% RANGE...WHICH IS ADEQUATE. SO
THINGS ARE POINTING TOWARDS A SUFFICIENT ADVISORY/NEARING LOW-END
WARNING EVENT. BORDERLINE QPF/DEEP LAYER SATURATION ARE CURRENTLY
THE LIMITING FACTOR TO NOT UPGRADING TO A WARNING AT THIS
TIME...AND THOUGH CONFIDENCE IS NOT QUITE THERE YET...SOME
ISOLATED HIGHER AMOUNTS ARE CERTAINLY POSSIBLE IN THE HIGHER
TERRAIN.
GETTING ONTO THE REST OF THE CWA...CURRENT SURFACE ANALYSIS DEPICTS
SURFACE LOW PRESSURE WELL EAST OF LAKE SUPERIOR AND WEAKENING. A
WEAK INVERTED TROUGH IS POINTED BACK AT OUR NW ZONES AND OUR INTO NW
MN...THOUGH LIGHT SNOW SHOWER ACTIVITY HAS BEEN CONFINED TO THE RED
RIVER VALLEY ASSOCIATED WITH A FEW DISTURBANCES MOVING SOUTH
UNDERNEATH A VERY COLD...SLIGHTLY POSITIVELY TILTED UPPER LEVEL
LOW. A FEW FLURRIES HAVE CREPT INTO OUR WESTERN AREAS. FAIRLY
STEEP LAPSE RATES A WEAK WITH 500H TEMPS OF -30 TO -36 OVER OUR
AREA...-36 TO -40 IN NW MN...AND A WEAK FRONTAL INVERSION KEEP
MOSTLY CLOUDY SKIES IN THE FCST. THE PRESSURE GRADIENT OVER THE
AREA HAS ALSO LIGHTENED UP WITH THE LOW OFF TO THE EAST. A NICE
BACKWARD PROPAGATING WAVE HAS SETUP WITH NW FLOW ALONG THE NORTH
SHORE TERRAIN RIDGE...PROVIDING A BREAK IN THE CLOUDS ALONG SHORE
BEFORE WINDS EVENTUALLY VEER TO THE N.
TONIGHT...THE INVERTED TROUGH WILL WEAKEN AND SINK SOUTH WITH THE CORE OF THE
UPPER LEVEL LOW. WE HAVE MAINTAINED LOW POPS OVER THE FAR WEST AS
THE LOW SINKS SOUTH TONIGHT...TAPERING TO FLURRIES TOMORROW MORNING.
THE CORE OF THE SOUTHERN PORTION OF THE UPPER LOW BECOMES CENTERED
ON SOUTHERN MINNESOTA TOMORROW...WITH THE COLDEST TEMPS ALOFT OVER
THE NORTHLAND THURS/FRI. SO WE ARE LOOKING AT THE COLDEST DAYS OF
THE WEEK WITH HIGHS IN THE UPPER TEENS TO LOW/MID 20S. NW WI WILL
SEE ITS COLDER HIGHS FRIDAY...THOUGH BOTH DAYS WILL FEEL ABOUT THE
SAME WITH VERY LITTLE AIR MASS CHANGE.
THURSDAY AFTERNOON THROUGH SATURDAY...THE SOUTHERN UPPER LOW PUSHES EAST
THURSDAY AFTERNOON INTO FRIDAY. SHORT RANGE MODELS BRING A
DISTURBANCE SOUTH THROUGH THE NORTHLAND ON THE NORTHERN END OF
THIS LOW WHICH WILL TRIGGER SNOW SHOWERS/FLURRIES THURSDAY
AFTERNOON INTO EARLY FRIDAY MORNING. THEN ANOTHER DISTURBANCE
SWINGS SOUTH FROM CANADA ON THE HEELS OF THE NORTHERN EXTENT OF
THE UPPER LOW. THIS WILL TRIGGER ADDITIONAL LIGHT SNOW SHOWERS
MAINLY OVER NE MN FRIDAY INTO EARLY SATURDAY. WEAK RIDGING
ATTEMPTS TO BUILD INTO OUR SOUTHERN/CENTRAL ZONES ON
SATURDAY...WITH ARROWHEAD KEEPING A FEW SNOW SHOWERS.
.EXTENDED...SATURDAY NIGHT THROUGH WEDNESDAY.
SFC RIDGING MOVES INTO THE FA SATURDAY NIGHT WHILE UPPER LEVEL WAVE
DEPARTS. WILL LEAVE OUT A MENTION FOR LES ALONG THE SOUTH SHORE FOR
NOW AS QUESTION OF HOW MUCH DRY AIR FROM THE RIDGING PLAYS A ROLE.
MODELS DIVERGE IN THEIR SOLUTIONS FOR THE REMAINDER OF THE EXTENDED
PERIOD. THE 12Z ECMWF IS FAVORED AND HAS BEEN FOLLOWED. THIS
TRANSLATES INTO PERIODS OF -SHSN/FLURRIES/NO WEATHER INTO WEDNESDAY.
&&
.AVIATION...MVFR CIGS WILL GIVE WAY TO VFR CONDITIONS THROUGH THE REST OF THE
AFTERNOON. KHYR MAY ENCOUNTER SOME FLURRIES THROUGH THE TAF PERIOD
AS LAKE EFFECT CLOUDS MAY BE ENHANCED ENOUGH TO GENERATE THE
FLURRIES.
&&
.POINT TEMPS/POPS...
DLH 16 23 12 24 / 10 20 20 30
INL 10 20 12 23 / 10 20 40 30
BRD 17 25 12 22 / 20 20 10 20
HYR 18 25 14 23 / 30 20 20 20
ASX 20 26 18 26 / 60 40 20 30
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...LAKE EFFECT SNOW ADVISORY UNTIL 10 PM CST THURSDAY FOR WIZ003-
004.
LS...SMALL CRAFT ADVISORY UNTIL NOON CST THURSDAY FOR LSZ121-146>148.
&&
$$
SHORT TERM: DONOFRIO
EXTENDED/AVIATION: GSF
