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Area Forecast Discussion

000
FXUS63 KAPX 292006
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
406 PM EDT Sat Apr 29 2017

.NEAR TERM...(Tonight through Sunday)
Issued at 401 PM EDT Sat Apr 29 2017

...Rain Tonight, Heavy Rain Sunday...

High Impact Weather Potential...Heavy rain is expected tonight 
through Monday morning across Northern Lower Michigan...which could 
lead to minor flooding and ponding of water.

Pattern Synopsis/Forecast...Warm front is stretched out from the sfc 
low in NE Texas to the Mid-Mississippi Valley. From the mid-
Mississippi Valley the baroclinic zone splits with the main warm 
front still in Indiana and Ohio while the second one follows the 
inverted sfc trough into the Upper Great Lakes which is beginning to 
push the sfc high in Lake Superior to the north. Models show that 
this will continue into the night and the baroclinic zone in Indiana 
and Ohio will rejoin the separated portion in N Lower. By 06z, the 
precipitation will be around Saginaw Bay and remain there as the 
warm front stalls until 12z. From 12z/Sun to 00z/Mon, the warm front 
begins to move north, slowly with the another 500 mb jet max moving 
up over it. This will bring another wave of rain north. 

Primary Forecast Concerns...As long as the convection along the warm 
front doesn't disrupt the southerly flow into the warm front then 
the heavy rain that the models have been advertising will occur. 
This can happen, but based on the current composite radar over 
MO/IA/IL, the heaviest stratiform rain should continue its path 
northeast into N Lower and looking at the slope of the cold front at 
this point, intervening convection shouldn't fire up south of the 
warm front. SREF and GEFS QPF plumes continue to show the best 
clustering around the mean which after 48 hours looks to be around 
2.25" roughly from near HTL to around APN. 

&&

.SHORT TERM...(Sunday night through Tuesday)
Issued at 401 PM EDT Sat Apr 29 2017

...Wet period of weather ahead...

High Impact Weather Potential: Early week river response to long 
duration moderate to heavy rain event that unfolds tonight through 
early Monday.
  
Pattern Synopsis/Forecast: One impressive deep layer moisture plume 
will be well established across the area Sunday night as well 
advertised deep layer trough and attendant surface reflection move 
northeast across the western Lakes. Both surface and mid level 
configurations are primed for a direct northward feed of Gulf of 
Mexico moisture, a fact well evident by guidance progged overhead 
precipitable water values spiking to 1 to 1.5" levels by Sunday 
evening. Quick look at the SPC sounding climatology page puts this 
in some rather rare air, well above the 90th percent tile and 
pushing near all-time record amounts for the date. Forcing to work 
over this moisture plume is impressive indeed, with forced mass 
convergence on nose of 50+ knot low level jet aimed right at 
northern Michigan, itself collocated nicely with tightening elevated 
frontogenetical response ahead of slow northward advancing surface 
warm front. Embedded thunderstorms within narrow elevated cape axis 
and a respectably deep warm cloud environment will only enhance the 
heavy rain potential. Corridor of deepest forcing and moisture 
pinwheels northeast out of the area on Monday. Slow passage of main 
trough axis will continue the shower threat (albeit of much lighter 
intensities) right through Tuesday.

Primary forecast concerns/challenges: Emphasis remains on rain 
amounts and what impacts the associated runoff will have on area 
rivers.

Details: Rounds of rain, at times moderate to heavy (especially with 
any embedded elevated thunderstorms), will continue across the area 
Sunday night. SREf plumes continue to target much of northern lower 
Michigan for the heaviest rain amounts, that when combined with 
tonight's and Sunday's anticipate rain, yield mean totals of 2 to 3 
inches for much of the area. Do feel the areal extent of these 
heavier amounts is likely overdone by quite a bit, but even most low 
end sref members show amounts in excess of an inch, which is rather 
rare for such a large data set. Still some uncertainty exactly where 
the heaviest rain axis will reside, with some fluctuation both north 
and south noted in dprog/dt's of the high resolution and sref 
guidance progs.

Still looks like the heaviest rain threat exits fairly quickly 
Monday morning as surge of deepest moisture and low level jet 
forcing push east of the area. Rapid approach/passage of mid level 
dry slot may bring a brief respite in the wet weather for a time 
Monday. However, the return of deeper moisture as intense mid level 
low rotates across the area later Monday through Tuesday will 
reintroduce the shower threat. Definitely not expecting too much 
additional rain during this period, with the greatest amounts 
(likely remaining at or under a quarter of an inch) focused in the 
favored upslope enhancement areas of northwest lower Michigan. Cold 
air advection ramps up through the period, resulting in a chilly and 
windy period of weather. Not completely out of the question for a 
bit of snow to mix in with some of the showers by Tuesday morning, 
but shouldn't be a big deal for sure. 

Flooding concerns: While rain will no doubt fall heavy at times 
Sunday night into early Monday, especially with any embedded thunder 
activity, this does not look like a flash flood scenario as the 
deepest convection looks to remain well south of our area. Northern 
Michigan's sandy soils are notorious for being able to absorb a 
tremendous amount of water, with the much less than anticipated 
rains from the previous event only helping the soil absorbing cause. 
Still, if rain amounts are as much as currently advertised, some 
ponding of water will occur, and those more susceptible river basins 
(the Rifle and Manistee rivers in particular) will likely approach 
or exceed flood stage. Latest river forecasts out of Minneapolis 
indeed puts the Rifle river near sterling well above flood stage 
early next week, and gets the Manistee river near Sherman awfully 
close to it. A touch too early for any type of warnings, and simply 
not seeing enough evidence to support an area flood watch. A 
refreshing of the earlier issued hydrologic outlook will suffice for 
now, as will a continued mention in our latest hazardous weather 
products and graphics.

&&

.LONG TERM...(Tuesday night through Saturday)
Issued at 401 PM EDT Sat Apr 29 2017

We may be dealing with just a little bit of lingering moisture at
the start of our period...in the form of a few drops or 
flakes...but nothing of real note. The "big system" will be 
through us and we will be quickly trending drier on Wednesday. 
Quieter weather 
*should* persist through the extended...with temperatures moderating 
to climo by Friday.  The fly in the ointment will be a system 
passing to the south, which models do not yet agree on.  The euro 
has this low moving up over Lake Erie and brushing our eastern areas 
with a little wrap around moisture on Friday...whereas the GFS keeps 
the track south.  That said, the GFS shows a weak clipper dropping 
down, providing some weak pops for Friday (which would explain why 
it tracks the southern system more southerly), but the euro gives 
this clipper little attention...washing it out as it arrives and the 
aforementioned southern low steals it's support.  Regardless...this 
is a long way off and will likely change several times before 
then...stay tuned.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 152 PM EDT Sat Apr 29 2017

Timing the rain in, and the cigs to fall is the main concern for
this set of TAFs. Rain and low clouds are slow to make it north
for the time being as dry air from north flow continues over the
region. Winds will begin to veer to the east early this evening
followed by the cigs falling to MVFR categories some time after
06z, with MBL and TVC falling first then PLN and APN. The rain is
expected to be light most of the night, but increase in intensity
overnight/early Sunday morning. With the heavier rain on Sunday,
fog will become possible late in the morning/early afternoon with
the rain. At this point, it looks like the VSBYS will still remain
MVFR, but the CIGS could be IFR or lower by 15z in portions of N
Michigan. 

&&

.MARINE...
Issued at 401 PM EDT Sat Apr 29 2017

Tonight through Monday...Winds this afternoon were around Small 
craft criteria for a period, but will probably drop them for new 
ones this evening, especially for the Lake Huron side as the ene 
winds begin to ramp up as the sfc low moves into the region. The ENE 
winds continue through Sunday, with some diminishing by the evening 
and overnight. Monday, winds veer south and remain under small 
craft criteria. 

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 8 PM EDT Sunday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 8 PM EDT Sunday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 8 PM EDT Sunday for LSZ321-322.
&&

$$

NEAR TERM...JSL
SHORT TERM...MSB
LONG TERM...KAB
AVIATION...JSL
MARINE...JSL