Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 141144
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
644 AM CDT Mon May 14 2018

.UPDATE...
Issued at 640 AM CDT Mon May 14 2018

Updated to include 12z aviation discussion below.

&&

.SHORT TERM...(Today and tonight)
Issued at 245 AM CDT Mon May 14 2018

Surface analysis early this morning shows a pair of generally
east-west oriented fronts across NOAM: one extends from the TX/OK
panhandle region through the mid-Mississippi River valley region
into the mid-Atlantic states while the second is draped over
southern Canada, just north of the international border. A surface
trough with a weak low pressure center meanders just to the south
of the Canadian front, from eastern MT into Lake Superior. Aloft,
the WFO MPX coverage area is caught between a deep cutoff low
over the Intermountain West and a deep ridge aloft over the
eastern GOMEX. A ridge axis emanating from the upper level high
extends NW into the upper Mississippi River Valley but several
shortwave disturbances over the Central Plains to the southern
Great Lakes are allowing convection to continue overnight.

At play for this area for today through tonight will be the
southward moving surface trough to the north and an upper level
shortwave disturbance currently over CO/WY. This shortwave will
traverse east-northeast into the upper Mississippi River valley
while moisture deepens in the mid-to-upper levels. The spread of
moisture looks better than previous days as does the strength of
the trough features both at the surface and aloft. There are even
multiple indications of MUCAPE in the 500-1000 j/kg range for
eastern MN through western WI today. Since most of this CAPE is in
the mid-to-upper levels, this spells the potential for simply
weak elevated convection (as such, isolated weak thunderstorms)
this afternoon into this evening. The coverage of precipitation
looks a little better but timing and exact location of
precipitation is highly problematic due to the scattered depiction
of showers/t-storms on even high-resolution models. Have kept
pops in the chance/scattered range but this may well need
adjusting as radar trends evolve. The precipitation is expected to
wind down and shift to the southeast late this evening through
the early morning hours with no precipitation remaining by sunrise
Tuesday morning.

As tricky as the precipitation depiction will be, so too will be
high temperatures today due to the cloud/precipitation
complications. After temperatures start out in the low-mid 50s
this morning, will look for highs to have an unusual southwest-
northeast spread from the upper 60s to the upper 70s. The lowest
maximum temperatures will be found in southwestern MN and the
highest maximum temperatures in east-central MN into western WI.
The passage of the aforementioned surface trough southward through
the coverage area tonight will act a bit as a cold front with lows
early Tuesday morning from the mid 40s to mid 50s.

.LONG TERM...(Tuesday through Sunday)
Issued at 245 AM CDT Mon May 14 2018

Long term concerns are timing of cold front progged through the
area Friday night over the west and exiting the east Saturday.

Models in general agreement in overall warmup ahead of the cold
front moving into the west late Friday. We should see plenty if
sunshine and light winds as another slow moving high pressure
moves through the area through Wednesday. Winds will be light
Tuesday and begin to pick up some from the south/southwest Wednesday
afternoon mainly to the west. Although humidity will be low
Tuesday afternoon, winds will be too light for any significant
fire weather concern. This will be the same for Wednesday, though
dewpoints may increase a tad out ahead of the cold front over the
Dakotas. Wednesday should be the warmest day of the week, with
mixed temperatures yielding at least low-mid 80s over the cwa.
Thursday could also be warm, depending on timing of the front and
clouds/showers that develop along the boundary.

The thunder threat looks greatest with the frontal passage Friday
night into Saturday. The ECMWF is about 6 hours slower with the
front so will compromise thunder placement into Saturday. Models
raise MLCAPE values of 500-1000 J/kg, bulk shear 30-35kt and mid
level lapse rates around 7 C/km at the moment with the best
potential over the southwest Friday evening. Will continue to
monitor trends of the next couple days to see if the front slows
more.

Cooler air arrives for the weekend with highs struggling to reach
70 once again as the trough departs to the east and flow aloft
becomes northwest.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 640 AM CDT Mon May 14 2018

Clouds will steadily increase into upper level ceilings by late
morning while a few rounds of showers moves in from the south. Not
looking for much in the way of impact at this point so have opted
to keep mention within VFR conditions. That said,
coverage/intensity may be more than advertised with some isolated
CB/TS as well, mainly late this afternoon into the early evening
hours, which could put conditions as low as IFR. Will see how
radar trends evolve and adjust as needed. Winds will be
light/variable for much of this period.

KMSP...Will look for scattered showers to develop by mid-afternoon
and continue into the early evening hours. Have kept conditions as
VFR but conditions worse than that may easily develop within the
same timeframe.

/OUTLOOK FOR KMSP/
Tue-Wed...VFR. Wind light and variable.
Thu...VFR. Chc -SHRA late. Wind S 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

UPDATE...JPC
SHORT TERM...JPC
LONG TERM...DWE
AVIATION...JPC



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