Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 220220 AAB
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
920 PM CDT Sun May 21 2017

.UPDATE...
Issued at 920 PM CDT Sun May 21 2017

Large scale upper level circulation is centered somewhere west of
Thunder Bay late this evening, with several smaller scale
vorticity maxima rotating around the large scale feature. While
overall large scale forcing for ascent is not particularly strong,
sufficient deep layer saturation remains across the entire area
(per 00z KINL sounding and latest model objective analyses) that
even weak forcing is continuing to result in rather widespread
drizzle and a few areas of more concentrated light rain showers.
This will likely be the case through the night and into Monday,
with a slow improving trend beginning during the day tomorrow.
Very few changes were made to the going forecast this evening,
which has the current situation depicted rather well.

Recent reports from southern Ashland County in the past half hour
indicate that flood waters continue to very slowly recede across
the entire affected area. However, flooding persists in most of
the same areas with many roads still affected. Thus, we made the
decision earlier this afternoon to extend the flood warning for
Glidden and surrounding areas through Tuesday afternoon. No
additional impactful rainfall that should impede the improving
trend is expected, but given the amount of water that needs to
work through the system, it seems likely that high water will
persist in some areas and have at least some impact on the road
network for the next couple of days.

&&

.SHORT TERM...(This evening through Monday)
Issued at 339 PM CDT Sun May 21 2017

An upper-level closed low, along with a mid-level shortwave that`s
expected to churn over the area tonight and through Monday, will
persist over the region. For the rest of the afternoon and evening,
the associated sfc low pressure center, currently situated over
northwest Wisconsin and the U.P. of Michigan, will continue to
ascend to the northeast over central Lake Superior, and into south-
central Ontario Canada tonight. The Northland will remain under the
cyclonic flow from this upper-level low, so chances of rain showers
and drizzle will remain over the region. 21.12z GFS/NAM model
soundings indicate varying depths of saturation, which will be the
driver for where rain showers or drizzle will fall, but it appears
that drizzle will be more favored over our southern regions Monday,
including northwest Wisconsin. Some embedded lobes of positive
vorticity advection are progged at the mid-levels, which will
provide the support for the precipitation. The mid-level wave
undergoes a bit of a split, where a northern wave breaks off from
the primary shortwave, and advects over the region, lingering the
PVA forcing overhead. This will support higher chances of rain
showers over north-central Minnesota Monday afternoon.

A rumble of thunder is possible, mainly across the southern tier of
counties from Pine county to Price county Monday afternoon as low-
level lapse rates are progged to steepen. However, values of MUCAPE
across the south are quite marginal, with values generally between
50 to 100 J/kg. The CMC model is showing higher MUCAPE values of
approximately 200 J/kg over northwest Wisconsin, so can`t rule out a
thunderstorm or two, but not expecting any widespread convective
elements. The latest SPC general thunder mention has been brought
further north, mainly south of a Hinckley to Dairyland to Park Falls
line, so will include a mention of thunder for these areas. Not
expecting an all-day wetting rain - more of an off and on
shower/drizzle variety. QPF amounts tonight through Monday could
bring an additional 0.01 to 0.20" across the Northland, with the
highest amounts expected over north-central Minnesota.

.LONG TERM...(Monday night through Sunday)
Issued at 339 PM CDT Sun May 21 2017

The large upper low over Ontario will send one more shortwave across
the forecast area Monday night, keeping clouds and chance for
showers going over the area into Tuesday.  With the cloud cover and
the generally chilly airmass, temperatures will only get into the
50s to around 60 on Tuesday, with morning lows in the mid 30s to low
40s.

Tuesday night, and again Wednesday night there is potential for
clearing and drier air to move into the area from the north, and
with the north flow continuing, we are likely to have a cold night,
with lows around freezing possible, mainly in the Arrowhead.  There
may be need of a frost/freeze headline for one or both nights,
depending on cloud cover.

Upper level ridging builds into the area for Wednesday and Thursday,
which should bring us a period of drier weather with slowly warming
temperatures for both days.   This will not last though, and the
next large, slow moving upper low will spread cooler temperatures
and chances for showers into the area beginning Thursday night, and
continuing through much of the upcoming weekend.  Do not have a lot
of confidence in the specifics beyond Friday night though, as the
ECMWF is more progressive and more phased than the GFS, which splits
some shortwaves off the nearly stalled upper low through the
weekend, and looking unrealistic by Saturday night and Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 658 PM CDT Sun May 21 2017

Low pressure centered over western Lake Superior this evening will
continue to move only very slowly northeastward through the
period. Underneath the upper low, mainly MVFR visibilities and
IFR ceilings are expected to persist, along with periods of
showers for much of tonight. We do expect a very slow diminishing
trend to the precipitation. Some gradual improvement is expected
Monday, but we have delayed the rise in ceilings and visibility in
many locations by a few hours from the previous TAF issuance.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  39  54  40  52 /  50  40  20  40
INL  41  52  42  59 /  60  60  50  30
BRD  41  58  43  57 /  40  30  40  50
HYR  42  59  40  58 /  50  30  20  30
ASX  41  56  39  52 /  40  30  20  30

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

UPDATE...Miller
SHORT TERM...JTS
LONG TERM...LE
AVIATION...Miller


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