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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

                            
000
FXUS63 KMQT 161733
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
133 PM EDT Fri Aug 16 2019

.SHORT TERM...(Today and tonight)
Issued at 351 AM EDT FRI AUG 16 2019

An impressive shortwave tracking east across southern Minnesota and 
into west-central Wisconsin this morning has sparked off showers and 
thunderstorms, some of which have continued to lift northeast 
towards western Upper Michigan this morning. Lagging slightly behind 
is the main surface trough draped northwest to southeast across 
Minnesota. The main forecast concern for today is the showers and 
thunderstorms expected to increase in coverage later today as this 
shortwave lifts northeast across the region. 

Overall, thermal profiles don't look terribly impressive for 
widespread thunderstorm chances, especially given the increasing 
cloud cover and lack of steeper mid-level lapse rates. However, 
skinny CAPE profiles look to develop, which may lead to a few 
isolated thunderstorms in spots across the Upper Peninsula later 
today. Convection will lift northeast across the west half this 
morning, and then push eastward throughout the day. Late in the day, 
as the main shortwave trough lifts through, deep-layer shear will 
increase to around 30 to 35 knots, but given the lack of instability 
not expecting any severe weather at this time. While severe weather 
doesn't look like a concern today, locally heavy downpours will be 
possible, especially with any thunderstorm activity, as the main 
axis of PWATs between 1-1.5'' shifts overhead today. Along with 
ample large-scale lift today, along and ahead of the main trough a 
synoptically enhanced LLJ will pump in deeper moisture, thus 
providing more fuel for showers and thunderstorms. Given the 
stronger winds just off the surface, gusty winds may accompany some 
of the convective activity today. Given how dry it has been over 
parts of the Upper Peninsula as of late, this does look like a 
chance to receive some decent, soaking rainfall for the west and 
central parts of Upper Michigan. 

Tonight, lingering showers and isolated thunderstorms will exit the 
region as the main trough axis and large-scale lifts into eastern 
Ontario. No real strong push of cold air advection behind the trough 
axis; therefore, not expecting much in the way of a significant 
cooling trend.

.LONG TERM...(Saturday through Thursday)
Issued at 505 AM EDT FRI AUG 16 2019

A strong positive height anomaly building over the AK Peninsula and 
Aleutians will shift nw and n to far eastern Siberia/adjacent Arctic 
Ocean early next week. This will initially support a deepening trof 
over western Canada thru the weekend. Early next week, a portion of 
this trof will shift e underneath a positive height anomaly n and nw 
of Hudson Bay. Then as the main the positive height anomaly drifts w 
across eastern Siberia/adjacent Arctic Ocean, the western trof will 
also shift w to the Gulf of Alaska which in turn will result in a 
ridge developing over the Rockies into central Canada by midweek. 
Late next week into the weekend, looks like broad negative height 
anomalies will set up across AK/Gulf of AK into nw Canada while 
positive height anomalies set up over the western CONUS. This would 
support enhanced Pacific flow and the potential of a progression of 
shortwaves downstream across the northern CONUS. As for temps, 
normal to above normal temps will round out the weekend into early 
next week. Temps will then fall back blo normal mid week behind the 
aforementioned trof that shifts out of western Canada. If amplitude 
of the building upstream ridge over the Rockies toward central 
Canada is sharp, there could be quite a cool down midweek to provide 
a preview of fall. Probably looking at temps returning to at least a 
little above normal overall late next week as midweek ridging over 
the Rockies and central Canada shifts e. As for pcpn, nearly all of 
the fcst area would benefit from a good soaking rain or two. Over 
the last 30 days, a large portion of the U.P. is running at 50-70pct 
of normal pcpn with areas of the central and e under 50pct of 
normal. Going back 60 days, we're still looking at a good portion of 
the U.P. at 50-70pct of normal pcpn. Some rainfall will occur today 
with a few areas possibly seeing decent amounts. The next round of 
pcpn will occur on Sun as a trof swings across the western Great 
Lakes. Fairly well-defined shortwave within the trof will provide a 
focus for more significant pcpn which may impact the fcst area. 
Another shortwave approaching Tue may produce isold/sct shra. The 
mid week period will then be dry with mid-level ridging approaching 
and then moving across the area. A wetter period or at least more 
frequent bouts of pcpn may be in the offing beyond 7 days as 
enhanced Pacific flow into Canada/Pacific nw sends a progression of 
waves into the northern CONUS/southern Canada. 

Beginning Sat, showers from today's system should have exited e of 
the area by 12z. However, there may be quite a bit of low clouds 
lingering during the morning and perhaps some patchy upslope 
-dz. These low clouds will give way to sct-bkn cu during the day. 
There will be a weak shortwave swinging toward the western Great 
Lakes in the aftn. Not out of the question that this wave could 
generate isold late aftn -shra, but for now, left any mention of 
pcpn out of the fcst since some of the model fcst soundings suggest 
there will be a cap in place thru the aftn. 

Models are in decent agreement on the mid-level trof to move across 
the western Great Lakes on Sun. Main focus will be on a shortwave 
over the Plains that lifts into the Great Lakes on the front side of 
the trof. Nocturnal low-level jet in response to this wave should 
support a growing cluster of shra/thunder Sat night over the Plains 
with this pcpn lifting ne into the Upper Lakes Sun morning. Pcpn may 
reach the w and s central fcst area late Sat night. While exact 
track of the shortwave and associated convection is not certain yet, 
seems that the se half of the fcst area has best shot of getting in 
on a period of decent rainfall Sun morning under shra and some 
embedded thunder. Not expecting any svr storms with this activity as 
MUCAPE is only a few hundred j/kg at best. Whether this morning 
shra/embedded thunder exits soon enough to allow for some 
clearing/daytime heating to build instability for the potential of 
new tsra development prior to passage of cold front is uncertain. 
Right now, that looks doubtful. However, should enough instability 
build, 30-40kt of deep layer shear would support the potential of 
organized storms and svr risk. 

Looks like quiet, warm, dry weather will follow for Mon. Heading 
thru Tue/Wed, ECMWF has trended sharper with the building Rockies to 
central Canada ridge mid week. This in turn results in amplification 
of the trof shifting into eastern Canada, and thus sharp cooling mid 
week across the Upper Lakes. Could be a few -shra Tue as the 
associated cold front passes. If the ECMWF is on the right track 
with 850mb temps falling to 3-4C for Wed, it will be a fall-like day 
with highs in the 60s under considerable stratocu and probably some 
-shra/sprinkles. With the ECMWF ensemble mean showing 850mb temps of 
4-5C on Wed, the ECMWF is probably on the right track with the more 
amplified trof. If clouds clear out Wed night, may be talking frost 
potential for the interior w which would be closer to approaching 
sfc high pres. Dry weather/warming trend will follow for Thu into 
Fri.
&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 133 PM EDT FRI AUG 16 2019

Trough pivoting through U.P. of MI this afternoon/evening from SW to 
NE with band of moderate to occasionally heavy showers. Rain will 
end next 1-2 hours at IWD but pick up at CMX soon and at SAW after 
about 21z. So far no lightning in these showers so have kept TS out 
of all TAFs but would not be impossible for some VCTS this 
afternoon/early evening, especially at SAW. Fog development likely 
tonight at all three sites but unsure how dense. Have all three 
sites going into IFR. Some brief periods of LIFR are possible but 
was not confident enough to include it yet. Vis clears quickly as 
sun comes up tomorrow and end of TAF period is VFR across the board.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 351 AM EDT FRI AUG 16 2019

Winds over the lake are expected to stay at or below 20 knots for 
the majority of this period. It is not out of the question that high 
platform observation sites could see south winds gust upwards of 25 
knots on Sunday ahead of a cold front approaching from the west. 
Showers and thunderstorms are possible today and then again on 
Sunday, mainly across the west half and the east half, respectively.
&&

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

$$

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