Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 251028
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
628 AM EDT Tue Apr 25 2017

.SHORT TERM...(Today and tonight)
Issued at 314 AM EDT TUE APR 25 2017

Upper air pattern consists of a 500 mb trough over the Rockies and a
shortwave over the northern plains this morning. This shortwave
moves to the east into the upper Great Lakes this afternoon. The
trough over the Rockies moves into the northern plains late tonight.
Nam shows deeper moisture and 850-500 mb q-vector convergence
arriving this evening and remaining overnight. GFS and ECMWF show
this too. However, NAM looks to be too cold with sfc temperatures
tonight and did not use them for this forecast. Went with the warmer
temperatures of the GFS and ECMWF which keep the pcpn as all rain.
One other major change to the going forecast was to keep the dry air
in longer today and pushed the timing of pops back a bit with slight
chance only in the far west late today and then categorical pops
overspreading the area tonight. These were the only major changes
done to the going forecast.

.LONG TERM...(Wednesday through Monday)
Issued at 414 AM EDT TUE APR 25 2017

...Wet Wed into Thu with main question about extent of wintry
precipitation...

Deep troughing still on track to bring active weather midweek into
the weekend. Best chance for dry day is Fri with potential for dry
day on Sat as well. General trends favor less wintry precipitation
with system affecting most of Wed, though low-level cold air still
could lead to freezing rain or even snow Wed night into Thu morning
over far west. Most areas likely will see total liquid from midweek
system (Tonight into Thu) of at least 1 inch with some areas seeing
2 inches. That precip along with more precip later in the upcoming
weekend should push NWS Marquette total precip for the month into
the top 5 wettest April.

Lead shortwave on edge of large scale troughing will be lifting
across Upper Mississippi River valley on Wed morning with 995mb sfc
low vcnty of eastern IA. Large scale lift fm the shortwave and
convergence fm the sfc low, along with h85-h7 moisture transport
into Upper Great Lakes/pwats 2-3 SD above normal will combine to
support widespread rain. Rain will be enhanced further by coupled
jet structure with jet streak over northern Ontario and other jet
lifting to the north-northeast from the Central Plains. Signal that
rain lets up late Wed morning into early Wed aftn as initial
shortwave lifts north of Lk Superior and primary shortwave is still
well upstream over central plains. Could be drizzle but moisture
depth is not too shallow so will just keep with rain mention to keep
it simple at this point.

Was completely on board with ptype staying all liquid until late Wed
night into Thu morning but latest ECMWF which had been more
consistent in showing a farther west and warmer solution has thrown
in a curve ball and now cools sfc-h85 temps down much quicker late
Wed aftn into Wed night/Thu morning. Will trend toward the ECMWF but
not completely as that is quite a change in its thermal profile.
Result is fzra/icing over far west on Wed night changing to mainly
snow/rain on Thu (dependent on blyr temps at that point). Models do
seem to be in agreement, at least for now, that when thermal fields
favor fzra on Wed night heavier precip will be more focused over
cntrl and east forecast area where it will be sufficiently warm for
rain/no icing. Hints there that majority of rain could be convective
as it will be advected along and just east of sfc trough in area of
max moisture advection and where there is some elevated instability
forecast. Placed slight chances of thunder in for later Wed aftn far
scntrl and pushed this over much of south and east forecast area Wed
evening. Based on SI/s near 0c could see potential for more thunder
later Wed evening extending into the overnight over eastern forecast
area on nose of south to southeast 40-50 kt h85 jet. Last few runs
of calibrated SREF tsra probabilities from SPC would suggest this as
well.

With the rain falling Tonight into Wed and again Wed night into Thu
morning, will have to keep eye on rivers/streams. All this water
will be falling over areas that have seen 1-2 inches above normal
for the last couple weeks or roughly 200-300 pct of normal. 1 hr and
3 hr FFG is as low as 1.3 in some areas as a result. If rainfall
during this time falls heavily, then minor flooding issues would not
be out of the question. At the least would see significant ponding
of water on roads/low-lying/poor drainage areas.

Now returning to the cold side of things. As colder air works across
west to east with sfc low lifting north of Lk Superior precip extent
should diminish through the day on Thu. Best chance at some minor
snow accums would be over far west from IWD to CMX. WPC probs
suggest 1 maybe 2 inches. Temps over northwest and north central
forecast area will struggle to reach mid 30s on Thu with persistent
cold air advection as upper low slides across region.

Agreement building that most of Fri into Sat stays dry as strong low
pressure system takes shape over the southern plains. As the low
lifts across the Upper Great Lakes it could become quite strong with
00z GFS, ECMWF, GEM showing min MSLP of 980mb and max of a still
respectable 990mb. Widespread precip would occur and consensus of
thermal fields and latest WPC probabilities point to accumuating
snow to open the month of May. Best chances would be over western
forecast area though that will depend on exact track of sfc low.
&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 628 AM EDT TUE APR 25 2017

Under mid and high clouds, a dry low-level air mass will dominate
the area thru this aftn, allowing VFR conditions to prevail at all
sites. A sfc trof drifting se into Upper MI this evening will result
in deteriorating conditions as shallow cold air undercuts warmer air
and -ra develops.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 314 AM EDT TUE APR 25 2017

Northeast gales look to start up across west and central lake
Superior late today and continue through Wed evening. By late
Wednesday night into Thursday morning winds will begin to subside to
20 to 30 knots as winds become northerly. Late Thursday through
Friday, winds will further decrease to 10 to 20 knots as winds
become westerly. Winds of 10 to 20 knots are expected through the
weekend and into early next week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 8 PM EDT /7 PM CDT/ this evening to 11 PM EDT
     /10 PM CDT/ Wednesday for LSZ162.

  Gale Warning from 8 PM this evening to 3 AM EDT Thursday for
     LSZ264.

  Gale Warning from 7 PM this evening to 2 AM EDT Thursday for
     LSZ263.

Lake Michigan...
None.
&&

$$

SHORT TERM...07
LONG TERM...JLA
AVIATION...07
MARINE...07



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