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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
604 PM CDT Tuesday Mar 31 2015

Short term...(this evening through wednesday)
issued at 349 PM CDT Tuesday Mar 31 2015

Active weather pattern arrives tonight and Wednesday with several
weather concerns expected. Tonight...upper level ridging over The
Rockies shifts eastward across the plains. Strong warm air advection
builds over the region with a decent low level jet developing in the
early morning hours. Initially...surface winds will be fairly
light...however as the surface pressure gradient increases tonight
south winds will become breezy. With the warm air advection...low
temperatures will be seasonally quite mild in the upper 40s to middle
50s. Followed the warmer bias corrected models.

Middle level trough begins digging into the High Plains after midnight.
By daybreak on Wednesday...surface low pressure deepens in North
Dakota. A potent cold front arrives in our western counties around
middle morning and the Interstate 90 corridor midday. South winds
increase to near advisory level in southwest Minnesota and adjacent
areas during the morning. Along the Buffalo Ridge in
particular...winds are most likely will reach advisory levels so
went ahead and issued a Wind Advisory from 7 am to 4 PM when the
front clears the area.

Moisture transport begins in earnest in the morning...particularly
just ahead of the front where moisture pooling should allow
dewpoints to reach the 50s. Temperatures heat nicely ahead of the
front as well...with highs near 80 expected in our far southeast
corner. Instability increases in northeast Nebraska...northwest Iowa
and far southern Minnesota in the afternoon with the arrival of the
higher moisture and temperatures. NAM produces convective available potential energy as high as 3000
j/kg and steep lapse rates in the Sioux City through Spencer Iowa.
Capping will hold off convection in this area through the morning
until the arrival of the front should initialize convection. Shear
is decent but mainly unidirectional...and should support some initial
supercell development along the front in the early afternoon. As the
storms increase...these storms will become more linear and proceed
eastward across northwest Iowa through the afternoon. Expect severe
storms to contain up to quarter sized hail and wind gusts to 65 miles per hour.
Right now it looks like storms will initialize just to the east of
the Sioux Falls metropolitan area but if the front does slow a bit...this
threat may increase. For timing of probability of precipitation and quantitative precipitation forecast...mainly followed a
blend of the arw and Gem regional.

Long term...(wednesday night through tuesday)
issued at 349 PM CDT Tuesday Mar 31 2015

Consensus among the hi res models is that by 7 PM our line of
thunderstorms will be along and southeast of a Sioux City to Spencer
Iowa line. Localized heavy rainfall will be the main
threat...although still could see some severe wind gusts around 60
miles per hour as the line pushes southeast. Expect the storms to be clear of
the County Warning Area sometime between 9 and 11 PM. Will see partly cloudy skies
behind the front with lows dropping into the 30s and 40s. Expecting
a breezy and cooler Thursday...although still looking at highs in
upper 50s to middle 60s. Will be a breezy day with westerly winds 15 to
30 miles per hour...gusting around 35 miles per hour...strongest north of Interstate 90.
Given good mixing into dry air aloft...thinking dewpoints will be
lower than most guidance. This will introduce fire weather concerns
which are described below.

Cooler air advects in Thursday night into Friday...with 20s and 30s
for lows and highs only in the 40s and 50s. A wave will also be
tracking across the plains...but think any light precipitation
should stay south of the area. The weekend should generally stay
dry...other than a slight chance of a shower as a few waves pass by
Saturday night into Sunday. Saturday should see 50s and 60s...but
Sunday looks cooler on recent runs as the wave passing to our north
pushes some cooler air south. Thus lowered highs...with 50s and 60s
again likely.

Early next week has the potential to be more active as a longwave
trough settles into the western portion of the country. This should
help increase the chance for some rain across the area Monday into
Tuesday...possibly even some thunder. Still a ways out and models
will likely take some time to pin down details...but for now can
just say the rain chances should increase. Given that...would also
expect temperatures to be cooler. Currently consensus is 40s and 50s
for highs...but again this will likely have to be adjusted as we get
closer depending on timing and track of the approaching system.


Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 602 PM CDT Tuesday Mar 31 2015

Primary concern into the overnight hours will be with winds. A
breezy southerly wind will decouple within the next few
hours...and with stronger winds aloft building...will continue
with a low level wind shear risk across the terminals through early morning. We
will turn mixy again towards daybreak ending the low level wind shear risk. Winds
through the day will be very windy with a southerly direction

Convection chances will begin to increase after 3pm...especially
in the fsd/sux corridor. Highest probabilities for convection
take place near will introduce a thunderstorms in the vicinity for guidance


Fire weather...
issued at 350 PM CDT Tuesday Mar 31 2015

Red flag warning Wednesday generally for areas along and west of the
James River. Northwesterly winds will increase to 20 to 35 miles per hour
behind the cold front...with relative humidity between 20 and 25
percent. Further east...relative humidity values should be higher...although strong
winds should still allow for very high fire danger. During the
morning and early afternoon...southwesterly winds will be quite
strong across southwest Minnesota and portions of northwest Iowa
ahead of the front...with gusts around 45 miles per hour. Current forecast
calls for relative humidity values around 35 to 40...but could possible be as low
as 25 to 30 percent if the moisture increase is slower than
expected. Thus while relative humidity should stay too high for red flag
conditions...given the strong winds...burning is not recommended.
Afternoon thunderstorms will likely produce a wetting rain across
northeast Nebraska...northwest Iowa and far southern Minnesota.

Another breezy and dry day on Thursday. Will probably end up
needing red flag headlines for a majority of the area...although
winds will be marginal in northwest Iowa and wednesdays rain may
suppress fire potential there. Generally looking at 15 to 30 miles per hour
winds with some higher gusts and afternoon relative humidity between 15 and 25
percent. Held off on a watch for now given its still a few days out
and we have warnings out Wednesday for a portion of the area.

The low relative humidity continues into Friday...around 20 percent...but currently
expect winds to stay low enough to avoid red flag
conditions. Although high to very high fire danger is still


Fsd watches/warnings/advisories...
South flag warning from 1 PM to 8 PM CDT Wednesday for sdz255-256.

Minnesota...Wind Advisory from 7 am to 4 PM CDT Wednesday for mnz071-072-080-



Short term...
long term...chenard
fire weather...chenard

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