Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 251211

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
711 AM CDT Tue Apr 25 2017

Issued at 653 AM CDT Tue Apr 25 2017

Updated to include 12z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 325 AM CDT Tue Apr 25 2017

Today and tonight...Surface analysis early this morning depicts a
low pressure center just to the west of WFO MPX this morning. It
associated warm front extends NE then E into northern WI while a
trailing cold front extends SW across northwest Iowa into eastern
Nebraska. The front then continues W to a stronger and more complex
low developing over the TX/OK panhandles. Scattered rain showers
overnight through east-central Minnesota due to enhanced isentropic
lift have shifted into northeast MN and northwest WI, allowing for a
break before more steady and heavier rains develop later today. The
cold front will have a slow progression eastward today while a
potent longwave trough aloft tightens, deepens and slightly pivots.
These actions will help kick the panhandle low northeast along the
front, allowing for enhanced omega in advanced of the cold front and
also bringing in plenty of additional moisture from the deep south.
Essentially, this entire frontal system will develop over central-
southern MN through central IA which will bring close to 1" of QPF
over the region (with potentially higher amounts) from late this
afternoon through tomorrow morning. Due to the lack of insolation
and fairly benign lapse rates, not looking for much at all in the
way of convection so the prevailing thinking is to have more
stratiform rains with an expected large precipitation shield
developing from south to north over the area. Have maintained pops
increasing to categorical levels for much of the WFO MPX coverage
area late today through tonight. The panhandle low will reach the
IA/MN/WI triple point by daybreak Wednesday morning with the front
just barely out of MN and bisecting WI. Thus, fairly little dry time
is expected this evening through tomorrow morning. The other
function of this system is to maintain the large temperature
difference across the area from west to east. Lows early this
morning are already at an over 20-degree difference from western MN
to western WI. This difference will continue today as temperatures
range from the mid 40s in western MN to the low 60s in eastern MN
with mid (to potentially upper) 60s in western WI. Since cold air
advection will not commence for the entire coverage area until
tomorrow, early Wednesday morning will feature another large
temperature spread with lows in the mid 30s to the lower 50s west to

.LONG TERM...(Wednesday through Monday)
Issued at 325 AM CDT Tue Apr 25 2017

The forecast concerns remain movement of the upper low across the
area Wednesday into Thursday and development of the next trough
over the western conus lifting into the region over the weekend.

Initially the trough is progged to lift northeast through this
period. Significant moisture should lift northeast Wednesday
morning with the first area of lift. What remains will be any
residual moisture Wednesday afternoon into Thursday as the closed
core low lifts slowly northeast. This should provide a very cool
boundary layer across the region by late Wednesday night. Any
remaining precipitation would be a rain and snow ix or plain snow
showers. We do have some wet accumulations progged for the far
northwest - around Alexandria/Staples area - which could see some
accumulation on grassy areas into early Wednesday morning.
Otherwise and mix/change over to snow would occur Wednesday night
into Thursday which would affect mainly the northeast cwa. Any
accumulation would be less than an inch.

The GFS still works another weak wave into the region Friday and
may affect mainly the southern cwa. We will retain the small
chance PoP for that region into Friday night. Then models and in
fair agreement with the next significant storm system to affect
the region over the weekend. Timing would favor later Saturday
night into Sunday night diverge more on the development and
handling the weekend storm system. The ECMWF is slower and more
dynamic/colder with the low. This would likely generate a rain
changing to wet snow scenario over much of the eastern cwa later
Sunday/Sunday night. The latest CIPS analog mean snowfall for that
period favors at least a couple inches of snow across the
northern half of the cwa or central Minnesota into west central
Wisconsin. Stay tuned.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 653 AM CDT Tue Apr 25 2017

A cold front currently in south-central MN associated with a low
pressure center just east of KMSP is expected to slowly progress
eastward across MN into WI tonight. A stronger secondary low
pressure center over the central Plains will ride northeast along
the front tonight through tomorrow morning. This system will be
responsible for deteriorating flight conditions and fairly
persistent rain this afternoon through tomorrow. On the backside
of the front, KAXN-KRWF are already showing LIFR/VLIFR fog along
with only 200ft ceilings. Though the fog is not expected to
progress much further east, the lower ceilings will eventually
take over all the TAF sites with the frontal passage with winds
swinging around to NW and N later today. Rain will be more
stratiform than showery but no thunder is expected. That said,
IFR-or-worse conditions will prevail from late this afternoon
through tomorrow morning at all sites. While confidence is high
that those low conditions will be realized, it`s a matter of
how/when those conditions are met. There may well be some timing
issues with the rain and/or degraded conditions which could force
fairly frequent amendments.

KMSP...Will look for MVFR ceilings to move into the area of KMSP
just prior to the next routine TAF issuance, at which point some
showers are also possible. Better chances for rain come in mid-
afternoon and continue to increase through tonight with high
confidence of rain by late afternoon. The timing of the rain could
impact the timing of the lower ceilings but confidence remains
high that IFR conditions will be realized by the evening rush.

Thu...MVFR likely, IFR possible. Chc -RA/-SN early. Winds N 5-15
kt bcmg light & variable.
Fri...Mainly VFR. Winds NW 5-10 kt.
Sat...Mainly VFR. Winds NE 5-10 kt.




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