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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1157 am CDT Wednesday Oct 1 2014

Update...for 18z aviation discussion below

&&

Short term...(today and tonight)
issued at 343 am CDT Wednesday Oct 1 2014

Surface analysis this morning shows a compact 995 mb low near Rugby
/ND/ with a trailing surface cold/occluded front down through the
central Dakotas that eventually works into the eastern Texas Panhandle. To
the east...high pressure continues to slide across Ontario...but dry
southeast winds emanating from it have really impeded the development of
precipitation across the mpx County Warning Area...to this point anyways. Aloft...the
feature of interest shows up nicely on water vapor imagery moving
into western Kansas...and this wave will be over southern Minnesota by the afternoon.

Southeast winds emanating from the Great Lakes high has held surface dewps in
the 40s across eastern Minnesota/western WI through the night...which combined with
the initial short wave and its forcing going due north through the
Dakotas and into southern Canada...bypassing the mpx area to the
northwest...resulted in the mpx County Warning Area remaining mainly dry through the night.
However...as the Kansas wave approaches...continued height falls out
ahead of the wave will allow precipitation to Blossom across the eastern half
of the mpx area within the zone of greatest ascent within the
low level jet...which will be working up through western WI. Hi-res reflectivity
forecasts certainly bear the look of a limited thunderstorm activity
forecast...so have continue to hold a thunder mention through the
day at isolated. Good model agreement in terms of quantitative precipitation forecast with a good
half to one rain of rain falling today along/east of the I-35
corridor. As a result...used a pretty much even model blend for
quantitative precipitation forecast...which resulted in the desired half to one inch amounts. Of
course with this amount of rain falling into an airmass with dewps
currently in the 40s...it will not warm up much today...so cooled
highs across eastern Minnesota/western WI...keeping them mainly in the 50s.

Out in western Minnesota...did introduce some low chance probability of precipitation out there this
afternoon. This is in response to the threat for seeing isolated-scattered
showers/storm developing along the cold front...which will be
entering western Minnesota during peak heating. Most guidance points to some
breaks developing by the afternoon out west...which will allow
temperatures to warm into the 70s. The NAM shows 500-1000 j/kg of
MLCAPE working east with the front today...so felt some 20/30 probability of precipitation
were warranted out west with the hrrr showing a line of showers
developing along the front by the afternoon and the 01.00 European model (ecmwf)
showing a narrow band of light quantitative precipitation forecast out in western Minnesota along the boundary
as well.

For tonight...dried out the entire County Warning Area after 6z as the Kansas wave will
be well off into northern Minnesota by then...with any activity along the front
losing interest with the loss of daytime heating. By 12z Thursday...this
boundary will be near the Minnesota/WI border. Winds will be calm/light
along and ahead of the boundary...so we will likely have to watch
for the development of low stratus and fog across eastern Minnesota/western WI
Wednesday night.

Long term...(thursday through tuesday)
issued at 343 am CDT Wednesday Oct 1 2014

The most active period in the 7-day forecast is the Thursday-Friday
time frame with a deep trough dropping south out of British
Columbia and Alberta that is expected to phase with the trough
currently over Montana/ID/NV by Friday afternoon. We delayed the onset
of precipitation on Thursday to include a more defined break in the
precipitation between the system currently in place across the upper
Mississippi River valley and the one expected late this week. This
entire system has slowed over the past couple days and there has
also been an eastward trend in most of the guidance. The 10.00z
NAM was the farthest west and thus wettest solution for the
forecast area...but even the 10.06z guidance has shifted east -
although the NAM still has really good fgen and heavy banded
precipitation in western WI and far eastern Minnesota Friday morning. There was
also an eastward shift with 10.00z European model (ecmwf). The GFS sort of splits
the difference between the NAM and European model (ecmwf). The uncertainty with the
precipitation locally is due to the developing dry slot with most of the
precipitation potentially sliding east. Even if most of the precipitation
slides east Thursday night and Friday morning...the potent upper
wave should produce light to moderate showers across the forecast
area on Friday. This will be coincident with strong cold advection
and strong winds during the day.

Friday looks quite blustery and we are now thinking many locations
might not even hit 50 for a high. The gusty winds...clouds and
light rain will make the upper 40s feel even cooler. Speaking of
the wind...we will likely be within 5-10 miles per hour of Wind Advisory
conditions across western Minnesota. The pressure gradient will tighten
as the surface low deepens over the Great Lakes and a high builds
in the northern plains. The speed of the mslp pressure falls is
not well agreed upon amongst the NAM/GFS/ECMWF. The cips analogs
for Friday are not very convincing for Wind Advisory...but still
show plenty of wind and also match many October days where Minnesota/WI
stayed in the 40s for highs. Nonetheless...we have sustained 25-30
miles per hour with gusts to 40 miles per hour in the forecast for Minnesota simply based on
the NAM and GFS forecast soundings showing really good mixing with
the cold advection and 40-50kts at 850mb by 00z Saturday.

For the most part we think the coming weekend will be dry...but
still quite cool. There has been some runs showing shortwave
energy dropping down from Canada along the backside of longwave
trough which establishes itself over upper miss...Great Lakes and
northeast US early next week...however...a vast majority of the
precipitation should remain attached to the core of the trough where
there is much better lift. The GFS and European model (ecmwf) diverge next week
with the GFS keeping the trough anchored and the European model (ecmwf) being much
more progressive in building heights.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1158 am CDT Wednesday Oct 1 2014

The trough over North Dakota that has facilitated a solid area of rain
showers over central/eastern Minnesota and western WI along with LIFR/IFR
conditions will lift north across Manitoba during the taf period.
Periodic waves of shortwave energy and weak surface troughing will
maintain reductions to flying conditions through the period. In
the wake of the showers this afternoon...the concern will shift to
the potential for fog development and stratus through the
overnight hours. The ceilings look to be the worst for west central WI
sites...where LIFR and even vlifr conditions are expected to
develop overnight. Conditions will be slightly less impactful with
westward progression toward kaxn/kstc/krwf.

The next slug of moisture and robust lift arrive on Thursday
afternoon and evening...primarily affecting kmsp/krnh/Keau...with
kstc and krwf on the western fringes.

South-southeast winds gradually veer tonight...with northwest
winds expected for Thursday. Speeds generally around or under 6
kts through the period.

Kmsp...
ceilings are admittedly tricky for this afternoon/eve. Expect the area of
rain to exit the Airport by 20z. There will be the potential for
scattered breaks in the sub-1000ft deck this afternoon...but overall
ceilings should remain below 1700 feet through 22z. Will then have a
window of time until 02z when ceilings could improve to ovc020...but
then should drop back to around 1500ft around/after sunset and
remain IFR overnight. Fog is expected to develop overnight...with
pockets of 1/2sm visibilities near the Airport. Not confident if kmsp
will go that low directly at the site...so will stick with 1sm
prevailing for now.

/Outlook for kmsp/

Friday...mainly MVFR with chance -shra. Winds west-northwest 20g30 kts.
Sat...VFR. Winds northwest 10-15 kts.
Sun...VFR. Winds northwest 10 kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$



Short term...mpg
long term...clf
aviation...ls

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