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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

                            
000
FXUS63 KMQT 191137
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
737 AM EDT Mon Aug 19 2019

.SHORT TERM...(Today and tonight)
Issued at 507 AM EDT MON AUG 19 2019

Water vapor imagery and RAP analysis show wnw flow into the Upper 
Great Lakes resulting from a trof extending from northern Manitoba 
into the Great Lakes and low amplitude ridging over the Rockies. In 
the wake of the shortwave that passed during the night, a much drier 
air mass has swept into Upper MI. This is clearly shown on the 
upstream KINL sounding which showed dramatic drying through the 
column from 12z Sun to 00z Mon. Precipitable water dropped from 1.22 
inches/148pct of normal to 0.53 inches/65pct of normal. So, clear 
skies are the rule across Upper MI early this morning. With dry air 
mass enhancing cooling, temps at interior cold spots have fallen 
into the 40s with some of the traditional cold spots down into the 
lwr 40s as of 08z. Temps range up to around 60F along Lake Superior. 

A sunny day is on the way today as dry air mass lingers. Main 
concern is drying potential with regard to fire wx. Incorporating 
some of the drying from mixed layer building into drier air aloft, 
expect dwpts to fall into the low/mid 40s F today. However, 
potential is there for dwpts to fall into the upper 30s F where lake 
moderation does not occur...over the interior w half in particular. 
Dwpts slipped just blo 40F at some locations in northern MN late 
yesterday aftn, lending support for that potential here today. With 
high temps in the mid 70s to lower 80s, minimum aftn RH will fall 
off to around 30pct. Due to high pres moving from se MN to Lower MI, 
winds today will be strongest over the nw part of Upper MI where 
gusts up to 20mph are expected, up to 25-30mph over the Keweenaw. 
Fortunately, that area received a good rainfall yesterday to lessen 
fire wx concerns. Portions of central Upper MI are a little more of 
a concern as not much rainfall occurred yesterday, conditions are 
abnormally dry (D0 on the drought monitor), and winds will be 
gusting to 15 to 20mph today.  

Dry weather will continue tonight. Push of isentropic ascent 
currently across se Manitoba into adjacent northern Ontario will 
shift e today and tonight. While it may support some isold -shra nw 
of Lake Superior today, main push of this isentropic ascent passes n 
of the area tonight and weakens. In addition, column remains quite 
dry tonight, so pcpn won't be a concern here. Shortwave moving 
across Saskatchewan/Manitoba will generate convection well nw of 
Upper MI tonight. This activity may approach Lake Superior by 12z 
Mon. Increasing precipitable water and stirring winds will lead to 
warmer night tonight than what is being observed early this morning.

.LONG TERM...(Tuesday through Sunday)
Issued at 355 AM EDT MON AUG 19 2019

...A TASTE OF FALL ON THE WAY LATER THIS WEEK...

On Tuesday, models have trended slower with the arrival of a cold 
front from the northwest. As a result, did lower PoPs quite a bit 
and adjusted dewpoints down as models all show better mixing, and 
tapping into lingering dry air aloft. While breezy southwest winds 
will prevail, thankfully sustained winds and RHs don't look to reach 
thresholds for fire weather concerns at this time. If the front 
slows down more, and stronger mixing does develop RHs may drop lower 
then currently forecast. While PoPs were cut back, it is still 
possible that we could see showers and thunderstorms across part of 
western Upper Michigan late in the day. Out of all the models, the 
GFS is the quickest to bring precipitation into the area, compared 
to the rest of the medium-range guidance and the tail-end of the 
high-res models. Some of the models show an area of convection 
developing early Tuesday morning and tracking east across north 
central Lake Superior, if that solution were to come to fruition 
there could be additional boundaries around to help foster the 
development of convection later in the day across the Keweenaw 
Peninsula. 

Tuesday night, the main cold front will continue to drop southeast 
across the region, flipping winds around to the northwest by 
Wednesday morning. As the front progresses across the region, models 
do show some lingering convection along the front. While we will 
lose diurnal heating and surface based instability overnight, there 
could be some lingering, limited instability ahead of and along the 
front. Enough to at least keep some mentions of thunder. Unless the 
front slows down further, it looks like the front will clear the 
Upper Peninsula by daybreak Wednesday. Behind the front, breezy 
northwest winds will move in and the start of a cooling trend. 

Wednesday through Friday morning, below-average temperatures will 
overspread the region bringing with it fall-like weather as high 
pressure builds in behind the front. In fact, daytime highs by 
Thursday may struggle to reach the upper 60s UP-wide. Overnight lows 
will be chilly each morning, with lows dropping into the 40s across 
the interior and 50s near the lakeshores. The coldest temperatures 
are expected Thursday night/Friday morning as surface ridging moves 
overhead. It is not out of the question that we could see a few 
spots across the interior west drop into the low to mid 30s early 
Friday morning. If these model trends continue, there could be a 
chance for some patchy early-season frost across the interior west. 

Ahead of the stronger surge of cold air advection expected to move 
in on Thursday, medium range models are hinting towards the potential 
for some shower activity across the east. For now, have just 
included silent PoPs for that time period, but down the road PoPs 
may need to be added. Otherwise, dry conditions will prevail mid-
week through the end of the week with no major precipitation 
concerns. With the arrival of cold air advection, breezy northwest 
winds are expected, especially Wednesday into Thursday as the 
surface pressure gradient will also play a role in boosting winds at 
times. 

Friday through the weekend, and into early next week, we will see a 
gradual warming trend as ridging slides east of the region and we 
find ourselves back under southwest, return flow. This warmup 
doesn't look terribly impressive, but we will return to slightly 
above-average temperatures. Both the GFS/ECMWF trying to bring 
convection into western Upper Michigan on Saturday as a shortwave 
lifts northeast across the Upper Mississippi Valley. However, models 
are showing a trend we've seen as of late with precipitation running 
into drier air and fizzling out as it reaches the Upper Peninsula. 
Therefore, the low-end PoPs loaded by the NBM seem reasonable for 
now, but wouldn't be surprised it PoPs continue to be pushed back in 
time. Another shortwave progged to arrive late weekend/early next 
week looks like it could bring the next best chance for widespread 
precipitation. While there is the potential, the track of this wave 
and resulting surface low will determine where that precipitation 
will track across the region.
&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 736 AM EDT MON AUG 19 2019

Under a dry air mass, VFR conditions will continue through this fcst 
period at KIWD/KCMX/KSAW. By late morning, W to SW winds will become 
gusty to 20kt at KIWD and to 25kt KCMX.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 507 AM EDT MON AUG 19 2019

While winds will diminish today on the east half of Lake Superior to 
under 20kt, sw winds up to 20-30kt are expected over western Lake 
Superior, particularly btwn the Keweenaw and Isle Royale. Winds will 
then fall off to blo 20kt across the lake tonight into Tue despite a 
cold front passing during Tue aftn. A cool air mass will follow for 
Wed into Thu. With unstable conditions developing btwn the warmer 
water and cooler air moving over the lake, winds will likely reach 
the 15-25kt range at times, and perhaps gusting up to 30kt 
occasionally. High pres will arrive later Thu into Fri to bring 
diminishing winds.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

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