Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
552 am CDT Thursday Apr 24 2014
Short term...(today and tonight)
issued at 345 am CDT Thursday Apr 24 2014
Short term concerns are rain/thunder threat today into tonight and
the chance of wet snow across mainly the extreme northern portion of
the County Warning Area into tonight.
Water vapor imagery showing large area of enhanced clouds with
initial wave lifting northeast into southern Minnesota. Some
lightning associated with this...and based on best lifted indice's...this
should work into south central Minnesota and into a small portion of west
central Wisconsin this morning. Cold temperatures over the northern
periphery of the County Warning Area now...with some middle/upper 30s. As strong lift
moves into the region later this morning...both the NAM and the GFS
indicated a possible rain/snow mix developing over the northern
portion of the County Warning Area. The potwx tool did indicate small areas of
rain/snow into the late morning/afternoon. We did include a slight
chance of snow with the rain over that region into today.
Rainfall amounts of over an inch are possible over the southeast County Warning Area
through the day. This has been well advertised in the grids the
last few days/ the rain area will be affecting the morning commute
over the south east. Second area of thunder possible later this
afternoon over the far northwest County Warning Area. Models were indicating some
MUCAPES of around 500 j/kg by late afternoon as the upper
trough/cold temperatures aloft generate some instability. Mentioned some
isolated thunder over the northwest County Warning Area during the afternoon/early
evening. Afternoon temperatures will once again be held in the 40s
in the areas seeing more widespread rain...mainly eastern County Warning Area.
The upper trough swings east into tonight. Could see a rain
changing to snow scenario over the northeast portion of the County Warning Area
before the precipitation ends overnight. Didnt mention any
accumulation at this time with relatively warm ground.
Long term...(friday through wednesday)
issued at 345 am CDT Thursday Apr 24 2014
The positive note in the long term portion of the forecast is that
models are in better agreement than they were 24 hours ago. The
not-so-positive part is that they have converged on a solution
that features the marrying of the central Continental U.S. Closed low
with a low that back peddles west-southwestward from Quebec. What
this translates to is a prolonged period of temperatures averaging
10 to 15 degrees below normal...and an extended period of 20-30 probability of precipitation
littering the forecast... as the massive low overwhelms the
eastern half of the nation.
In the meantime...the forecast looks on track for moderating
temperatures to near climatological normals on Friday as weak
ridging builds in overhead upstream of the deepening Baja California trough.
Friday highs will range between 55 and 65 degrees across the
majority of the forecast area...with slightly cooler readings in
the lower 50s up toward Ladysmith where residual clouds and
isolated showers will linger.
Saturday will bring a strengthening easterly wind as the
aformentioned trough reaches the plains. Related precipiation
should begin expanding north and east across the area on Saturday
night...with notably increasing rain shower activity on Sunday
afternoon and evening into Monday as a nearly stacked system
meanders across Nebraska and Iowa. Have included 60-80 probability of precipitation across
the bulk of the area during this timeframe...excepting a Little
Falls to Eau Claire line which may be on the northern fringes of
the more organized precipitation. Southern Minnesota locales will have
the opportuninty for thunder...while northern areas /Interstate 94
and north/ may see some snow mix in /primarily in the nocturnal
Wednesday and Thursday feature the previously discussed low probability of precipitation
and cool temperatures...with near to slightly below freezing
readings possibly closing out the month of April.
Aviation...(for the 12z tafs through 12z Friday morning)
issued at 540 am CDT Thursday Apr 24 2014
Large area of rain lifting to the northeast across area through
the morning. This will bring widespread IFR conditions across most
of the area...through the morning...tapering off to the west this
afternoon...and spreading east into Wisconsin this evening. The
heavier rains will fall across the southeast portion of the forecast area
mainly this morning. Visibilities will be limited to around 2sm rain br.
Surface trough will swing east to near the WI/Minnesota border by 00z
Friday. This should improve the ceilings/visibilities to the west...but will
remain lower to the east into the night. Some threat of IFR fog
developing before the trough exits Wisconsin later tonight. Will
mention some MVFR visibilities there for now. This may spread to the
north and west...but believe enough dry air will drop in behind
that to preclude anything widespread. Should see VFR conditions
after that some morning fog/lower clouds into Wisconsin.
Southeast winds could be a bit gusty ahead of system exiting to
the east this morning. Otherwise...as the surface trough
departs...wind should become northwest/west and remain less than
10 kts overnight.
Kmsp...will continue IFR conds through the morning...slowly rising
to MVFR by afternoon. The rain should taper into the afternoon as
a surface trough moves through later this afternoon and turns the
east/southeast wind to more north/northwest by evening. This should break out
to the VFR conditions into the evening/overnight. There is a
chance of some fog developing later tonight/Friday morning if
winds die off completely. At the moment believe there will be
enough mix to preclude mentioning that for now.
/Outlook for kmsp/
Friday...VFR. West winds 10-15 knots becoming north.
Sat...VFR. NE winds 10-15 knots.
Sun...mainly VFR. MVFR conds possible in -ra. East winds 15-25 knots.