Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 182047

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
347 PM CDT Fri May 18 2018

.SHORT TERM...(This evening through Saturday)

Issued at 346 PM CDT Fri May 18 2018

Trend of decreasing precip potential with the incoming front
continues. The problems this front are encountering include weak
forcing in split flow, with the MPX area stuck between the northern
stream up in southern Canada and the southern stream down across the
srn/central Plains. We also lack much in the way of instability
thanks to dewpoints only in the 50s and meager mid level lapse
rates. And finally, the low levels remain quite dry ahead of the

Based on what we are seeing with the HRRR and other CAMs, looks like
we`ll see only scattered showers developing along the front as it
moves through tonight, with precip amounts for where it does rain
rather meager.

What we do look to get with the front is a good dose of post frontal
stratocu as what we see up in NODAK today moves through here tonight
and Saturday. This cloud cover along with CAA behind the front will
help hold highs back a good 10 degrees from what we are seeing
today. They also look shallow and unlikely to provide us with much,
if any precipitation.

.LONG TERM...(Saturday night through Friday)
Issued at 346 PM CDT Fri May 18 2018

The long term will start with southern stream wave currently coming
out of the 4-corners region slowly making a trip across Iowa and the
WI/IL border Sunday and Monday. There will be several bouts of
showers and storms beneath this wave, but those will stay largely
south of us. Our problem is the northern stream wave going across
southern Canada on Saturday will drop an area of high pressure over
central MN/northern WI. Dry air associated with the high will limit
the northern extent of precip Sunday/Monday, with the I-90 corridor
looking to have the best shot at seeing rain. Current PoPs probably
still spread precip chances too far north Sunday and Monday, but we
did see a southward contraction with this forecast update.

Behind this system it`s back to more of the same for what we`ve been
dealing with much of May. With the northern stream retracting well
north into Canada as an upper ridge builds from the northern high
Plains up toward eastern Alaska. A weak southern stream under-cuts
the ridge, coming out across the southern/central Plains. This
means highs in the 80s return Tuesday and will stay with us for the
rest of the work week. As heat/moisture slowly build next week,
models show increasing instability and start generating qpf based on
diurnal destabilization and nightly increases in the strength of the
LLJ. Current forecast is probably overdoing the endless precip
chances that start Wednesday as at some point Wednesday thru
Saturday you can find a model giving us precip, hence the forecast
that sounds a lot more active than it will really be. Best precip
chances look to come Friday/Saturday when there is at least some
agreement on a system working across the upper MS Valley, though it
does not look overly strong, with severe weather or even healthy
rainfall amounts looking unlikely.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 128 PM CDT Fri May 18 2018

Low confidence on whether or not we`ll see precip this period, as
best forcing for precip looks to go north and south of the MPX
cwa. Last couple of runs of the HRRR have been developing showers
along an advancing cold front across central MN, but will see if
this trend survives a couple of more runs before hitting the
threat for precip any harder than what we currently have with a
VCSH at STC. Beside the threat of showers, there is an expansive
area of IFR/MVFR stratus behind the front across NODAK and there
is broad model support that this stratus will sweep across MN
tonight behind the front, so introduced some MVFR cigs, similar to
what we are seeing with the HRRR/LAV. Beside the NODAK stratus,
there is also stratus down in IL/IN that will head this direction
on the southeast winds. Looks like western edge of these clouds
will make somewhere between Menomonie and Medford in WI, which is
why we introduced the 1k ft cig at EAU at 9z, though these clouds
could end up staying east of EAU.

KMSP...Shra/iso TS threat looks greatest between 6z and 10z, but
not enough confidence in its occurrence to include in the TAF at
this point. Model agreement is strong in low stratus coming in
behind the cold front. Will likely come in under 018, though think
IFR is unlikely.

SUN...VFR. Wind ENE 5-10 kt.
MON...MVFR. Chc -SHRA. Wind E 5-10 kt.
TUE...MVFR cigs early, then VFR. Wind lgt and vrb.




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