Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 291750
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
150 PM EDT Sat Apr 29 2017

.SHORT TERM...(Today and tonight)
Issued at 403 AM EDT SAT APR 29 2017

Expect a quiet weather day across the area as we remain under the
influence of high pressure. The 00Z RAOB from International Falls
shows a rather dry airmass upstream of the region that will spread
south across the area as high pressure crests the region. Onshore
flow near Lake Superior will keep temperatures on the cooler (low
40s) side near the lakeshore, but further inland, temperatures
should climb into the upper 40s and maybe pushing 50 across the
south central where downsloping winds will aid in warming.

Upper-level clouds will increase in coverage this evening and
overnight ahead of a low pressure lifting north out of the central
Plains. Precipitation chances will also return across the south
central and far eastern portions of Upper Michigan as 850mb flow
veer northerly to east/southeasterly and warm air advection returns
to the region. Based on temperatures profiles, looks like
precipitation may start off as a rain/snow mix, before transitioning
over to rain.

.LONG TERM...(Sunday through Friday)
Issued at 441 AM EDT SAT APR 29 2017

The active pattern that has brought frequent bouts of pcpn to the
fcst area over the last couple of weeks will continue into early
next week as one more significant pcpn producing system lifts into
the western Great Lakes. Some snow will occur as well. Once this
system passes, a large scale pattern change is in the offing.
Ridge/positive height anomaly currently off the W Coast will build
into the western CONUS by the middle of next week, shifting the
recent mean Rockies/Plains trof eastward and ending the train of ne
tracking shortwaves across the central CONUS. However, as the ridge
shifts e, one more shortwave will round it, dropping into the
Southern Plains/Lower Mississippi Valley during the middle of next
week. As was the case yesterday, it appears that the progession of
the large scale pattern should keep the storm system that this wave
spins up (another big pcpn producer) well se and e of the Upper
Lakes late next week. However, it will be something to monitor. If
the upstream ridge is sharper, leading to a more strongly digging
shortwave, the progression of the large scale trof will be held up
and the storm track could be much farther nw, or down the road, the
Upper Lakes could fall under the chilly influence of what becomes a
large cutoff low over the ne CONUS, a solution beginning to appear
in some guidance. As for temps, blo normal temps will prevail over
the next 7 days. Departures from normal for max temps will be most
notable early next with readings as much as 15-20 degrees blo
normal. Temps should trend upward during the last half of next week,
closer to normal, but that will depend on progression/amplitude of
the trof just discussed. Looking farther ahead, CFSv2 ensemble mean
fcsts continue to point toward overall blo normal temps thru mid
May. That doesn`t mean there won`t be some warm days, but rather
that the pattern shouldn`t support any longer periods of above
normal temps. It also appears that a drier pattern will be setting
in for the Upper Lakes.

Beginning Sun thru Mon...mid-level low centered vcnty of western OK
Sun morning will lift ne, deepening around 150m at 500mb, by the
time it reaches roughly central Upper MI Mon evening. Sfc low will
track from near Kansas City to central Upper MI. Weaker shortwaves
lifting nne btwn the mid-level low and a strong ridge near the E
Coast, 500mb positive height anomaly around 200m, will aid deep
southerly flow/abundant moisture transport into the Great Lakes.
Models remain in very good agreement that these waves and strong
moisture transport will support periods of heavy rainfall lifting
nne across Lower MI on Sun. While some rain should begin to spread
into the fcst area during the day Sun as isentropic ascent/moisture
transport begin to increase, especially s central/se, the main
period of heavier pcpn for Upper MI will hold off until the mid-
level low moves closer Sun night/Mon. Vigorous deep layer forcing
per q-vectors combined with strong isentropic ascent/moisture
transport and precipitable water increasing to above 1 inch/250pct
of normal will likely support a band of mdt/hvy pcpn swinging n
across the area later Sun night/early Mon morning. In addition, with
mid-level dry slot surging nne, not out of the question that there
could be a few rumbles of thunder on the backside of the mdt/hvy
pcpn band as it lifts n. Will probably see widespread 0.75 to 1.25
inch rainfall amounts across the fcst area by late Mon aftn. While
there have been some concerns about wintry ptypes as the pcpn
spreads into w and nw Upper MI, that concern is mostly gone. Only
the 00z CMC maintains a weak enough warm layer aloft that might
allow for wintry ptypes over the w and nw. For now, believe warming
will be sufficient to largely prevent any frozen ptypes. As the
strong isentropic ascent/moisture transport lift n of the area Mon
morning, followed by mid level dry slot, pcpn intensity/coverage
will diminish markedly. Deeper moisture will then fill back in over
the area throughout the day as mid-level low approaches, reaching
Upper MI Mon evening. Fcst soundings suggest ptype will remain just
rain thru the day Mon. Only possible exception may be the far w high
terrain around Ironwood, but even there, majority of guidance
supports rain as ptype.

As the mid-level low drifts across the Upper Lakes Mon night, then
lifts toward se Canada and opens up on Tue, lingering sharp cyclonic
flow shifting to the nw and persistent low-mid level moisture will
likely maintain areas of pcpn into Tue. This pcpn will begin to
diminish Tue aftn and more so Tue night due to arrival of drier air
and weakening cyclonic flow as system moves farther away. With the
wshft to the nw and arrival of colder air, rain will at least mix
with some snow, especially over the higher terrain of the nw half,
where there could be some minor snow accumulations, perhaps an inch
or two, especially during Mon night/Tue morning.

Should be able to slip in a dry day on Wed, then much will depend on
the evolution of the mean trof progressing toward the eastern CONUS.
As mentioned earlier, energy will be diving into the Southern
Plains/Lower Mississippi Valley mid late week ahead of the ridge
shifting into the western CONUS. Provided the low pres system that
develops from this energy remains well to the se, any pcpn late week
will be tied to additional shortwaves that may drop into the
amplifying eastern trof. At this time, it appears there may be a
shortwave passing on Thu that could generate isold/sct -shra.
&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 149 PM EDT SAT APR 29 2017

VFR conditions will prevail over the next 24 hours; however, there
may be lower clouds that try to build into the KSAW TAF site toward
the very end of the TAF period. There may be a few wind gusts this
afternoon as mixing increases through the day, but not expecting
much more than 15 to 20 knot gusts.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 403 AM EDT SAT APR 29 2017

Winds of 15 to 25 knots this morning will subside to 10 to 15 knots
as high pressure moves across the area today. By Sunday morning,
winds will become northeasterly ahead of an approaching low pressure
system from the central Plains. Winds will increase to 20 to 30
knots by Sunday afternoon. By early Monday morning, as low pressure
begins to lift across the Upper Great Lakes, northeast gales of 35
to 40 knots are possible, especially across the west and central
portions of the lake. The winds will begin to subside to 20 to 30
knots Monday night into Tuesday as the winds veer northerly. Winds
will further subside to 10 to 15 knots by Wednesday morning, and
will remain below 20 knots through the remainder of the week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Watch from late Sunday night through Monday evening for
     LSZ162-263-264.

Lake Michigan...
  Gale Watch from Sunday afternoon through Monday morning for
     LMZ221-250.

&&

$$

SHORT TERM...Ritzman
LONG TERM...Rolfson
AVIATION...KEC
MARINE...Ritzman



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