Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 160813

Area Forecast Discussion
National Weather Service Marquette MI
413 AM EDT Tue May 16 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 419 PM EDT MON MAY 15 2017

Large scale pattern features deep trough over western Conus with
flattening ridge downstream over middle Conus. Upper level jet is
present from the Rockies to south central Canada. At the sfc, main
low is in lee of the Rockies with warm front extending to southern
MN and southern WI. H85 trough is farther north across MN to western
Upper Michigan with main edge of higher h85 theta-e just west and
southwest of Upper Michigan. Warm and moist advection has brought
showers and isold tsra to west and southwest Upper Michigan through
much of the day. Parts of Gogebic county have seen over 1 inch of
rain and there was steady lighter rain into Ontonagon and Iron
county as well. Temps in those areas really were impacted with IWD
and LNL still in the 40s even at this hour. Elsewhere mid clouds
have spilled east gradually and temps have reached the 50s to near
70 degrees, warmest and driest over far east closer to departing sfc
high still over the lower Great Lakes.

Following radar trends and various short range convective allowing
models (CAMS), expect the area of showers over western forecast area
to slide toward central forecast area into early this evening.
Greatest elevated CAPE up to 1000 j/kg remains south and west of
Upper Michigan so widesread tsra not expected inot the evening for
most of Upper Michigan. Probably a better chance at seeing more tsra
over far west where upstream convection could slide across and since
that area is closer to higher h85 theta-e and elevated CAPE. Attn
later this evening is on convection lifting east north east out of
eastern MN. THis convection is firing along gradient of elevated
MUCAPE which RAP does show making a run into far scntrl forecast
area this evening. Have increased pops toward Menominee county.
Suppose there could be a few stronger storms make it that far north
but with greatest MUCAPE increase over southern WI instead of
farther north into WI, seems that the line of storms should tend to
weaken at least from a severe standpoint. Heavy rain certainly
possible this evening and heavier cores could also produce pea sized
hail with freezing levels around 10kft.

For later tonight, at least right now, models have trended toward
keeping most concentrated convection anchored closer to sfc warm
front lifting slowly north over southern MN to central WI. This
especially makes sense with the convection in the evening serving
to re- inforce cooling over northern WI which would help hold the
warm front to the south. Trimmed pops back after rain moves
through this evening. Do bring chance pops in late tonight into
Tue morning as the warm front tries to lift back to the north
running into h85 theta-e advection that will be ongoing along h85
front. Eventually whatever works through in the morning should
allow recovery in temps/humidity by Tue aftn with readings well
into the 70s and dwpnts nearing 60F over the west. Large scale
forcing will be minimal but the buildup of instability and any
warm air advection that focuses closer to the low lifting across
MN could lead to additional showers and thunderstorms especially
west in the aftn. SREF probabilities which keep severe probs well
to the south of here tonight show increase over west on Tue aftn.
SPC does have our western forecast area in marginal risk for
severe. Similar to tonight with the increasingly humid airmass,
all the tsra could produce heavy rain and will have to watch out
for any areas where tsra train over same areas.

.LONG TERM...(Wednesday through Monday)
Issued at 411 AM EDT TUE MAY 16 2017

Models indicate a shortwave lifting ne late tonight along a cold
front moving into western Upper Mi. This shortwave could sustain
convection along the front into west and north central Upper Mi
early Wed into Wed afternoon. The arrival of a more vigorous
shortwave will offer the potential of a more significant organized
pcpn event for the Upper Great Lakes later Wed night into early Thu.
After what looks to be a dry period on Fri, another shortwave and
associated sfc low is expected to lift out of the western CONUS
trough/southern Plains and bring another round of pcpn into the area
for the weekend. As for temps, after a preview of warm/more humid
summer type weather over the next couple of days, cool weather/blo
normal temps will return in the wake of the Wed/Thu system.
Progression of the mean trough to the Great Lakes/Mississippi Valley
early next week will then work to maintain an overall blo normal
temp regime for the fcst area thru next week.

Wed/Thu...A shortwave lifting ne across the cold frontal boundary
into western Upper Mi late tonight could sustain some lingering
showers/isold tsra across west and north central Upper Mi into Wed
morning/early afternoon despite fairly weak forcing (q-vector
convergence) depicted by models. Main attention will focus on
vigorous shortwave lifting ne thru the Plains on Wed, reaching
southern MN Wed evening and the Upper Lakes on Thu. Meanwhile as the
cold front drifts slowly se through Upper MI on Wed, the sfc low
pres associated with the approaching shortwave will lift along the
front Wed night/early Thu. With precipitable water running from 1.3-
1.5 inches or 250+% of normal, placement of the front will be
critical for determining where heavy rainfall will occur as the wave
lifts across the area. While model guidance is not widely varying,
there is enough difference in this critical feature that pinpointing
heavy rainfall area is not certain yet. For now, model consensus
suggests front will be setup across central Upper MI, supporting
best chance of heavy rainfall across western Upper MI late Wed into
Wed night. Certainly could see widespread 1-2 inches of rainfall
with some local 3 inch amounts. Instability looks minimal Wed into
Wed evening as it appears there may be considerable cloud cover.
Still, there will be the potential of severe storms near the cold
front as it drifts into central Upper Mi, conditional on whether
there will be enough breaks in cloud cover for heating/instability
to build up. Lingering rain will diminish Thu and probably end for
most locations by evening. Max temps on Wed may show a large range,
depending on location of the cold front. May turn cool along Lake
Superior behind the cold front (temps falling into the 50s) while
remaining warm/humid (upper 60s/lower 70s) ahead of it. Thu will
turn much cooler across the area as low pres/cold front exit. In
fact, temps across the w and n may hold to or fall to the low/mid
40s during the day.

Fri thru the weekend...the GFS is quicker than either the CMC or the
ECMWF in advancing the Rockies upper trough out into the Plains with
lead ejecting shortwave energy bringing some shra back into western
Upper MI by Fri evening. ECMWF remains consistently slower, though
it has shown a slightly faster trend toward the GFS solution. Fcst
will lean toward the drier ECMWF solution for Fri. As the trough
shifts to the western Great Lakes by late Sun, sfc low pres will
lift into the Upper Lakes over the weekend, bringing more shra. 00Z
models suggest a more westward track with sfc low with the model
consensus indicating the best chc of pcpn Sat afternoon into Sat
night. With models trending toward a more westward track, temps
should be a bit milder this weekend with highs in the mid to upper
50s. Drier weather should then return for Mon as the sfc low
lifts ne of the Upper Lakes and is replaced by weak high pressure.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1237 AM EDT TUE MAY 16 2017

Warm front associated with a low pressure system over the Western
Plains is expected to stay south of the area tonight into central
Wi and southern Mn which is where shower activity should stay
focused late tonight. A disturbance lifting northeast from the
Central Plains late tonight into Tue morning will push the warm
front farther north and could be the focus for another round of
showers and thunderstorms lifting toward the TAF sites on Tue
morning though exact timing is still uncertain. Also coverage of
showers will be uncertain as forecast soundings indicate
atmosphere may be capped by warmer air aloft which could limit
shower coverage or suppress it altogether. The rain which occurred
this evening along with nighttime cooling and east to southeast
winds north of the warm front should result in developing low
clouds and possible fog late tonight into Tuesday morning. MVFR
cigs and vsby seem likely in this setup with even an outside
chance of IFR conditions, especially at KSAW and KCMX with onshore
flow off the Great Lakes. Expect some improvement in cigs/vsbys
Tue afternoon with diurnal mixing and wind direction taking on a
more southerly component. LLWS will develop Tue evening across the
TAF sites as a low-level jet or wind max moves across the region.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 411 AM EDT TUE MAY 16 2017

Expect winds to increase today into tonight as a warm front lifts n
toward the area. Gusts should increase to 25kt over the eastern part
of the lake. After a period of lighter winds Wed morning as a sfc
trough settles over the lake, winds will ramp up Wed aftn thru Thu
morning as low pres rides up the trough across central Upper MI and
eastern Lake Superior. Expect ne to n winds to increase up to gale
force Wed night/Thu morning over western Lake Superior and late Wed
night thru early Thu aftn over central Lake Superior. Winds will
then diminish to under 20kt into Fri. There may some stronger winds
again this weekend as another low pres lifts into the Upper Lakes
but should remain well blo gale force.

Finally, combination of showers and increasingly humid air arriving
over the cold lake waters will result in fog developing today and
lingering thru early Thu. This fog may become dense tonight into Wed
night. The fog will dissipate with the arrival of drier air on
northerly winds late Wed night/Thu.

Upper Michigan...
Lake Superior...
Lake Michigan...


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