Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/13/18
Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
651 PM CDT Sat May 12 2018
.DISCUSSION...See Aviation section for 00Z TAFs.
.AVIATION...Boundary layer moisture is higher over the coastal
plains this evening where MVFR ceilings continue at this time.
Expect a brief period after 02z when clouds will scatter along
the coast. But expect an earlier onset of MVFR ceilings returning
for coastal areas between 05-06Z. Low level flow is not expected
to be as strong as last night especially over the Victoria
Crossroads. Patchy fog will be possible for the inland coastal
plains late tonight with IFR vsbys possible for VCT area. SREF,
HRRR models along NAM model soundings indicated lower IFR ceilings
possible for the coastal plains between 09-13Z. MVFR ceilings are
also expected to reach LRD area earlier around 08Z. MVFR ceilings
should continue through the morning hours into early afternoon
when VFR conditions will be prevalent area wide.
.PREVIOUS DISCUSSION... /Issued 237 PM CDT Sat May 12 2018/
SHORT TERM (Tonight through Sunday night)...
With the upper low over the North-Central Gulf of Mexico and high
pressure over Texas (at least by default), we should stay high and
dry (or should I say unseasonably warm and dry). Could not rule
out a rogue shower here or there (here near the Rio Grande early
in the short-term with the moisture axis present, then there
offshore with some moisture coming in from the gulf). In any case,
the main synoptic and high resolution models do not show anything
of significance, and thus no rainfall will be forecast. Winds may
be elevated this evening a bit as the sea-breeze pushes west (and
over the coastal areas tonight), which will help to keep some
temperatures up again. Could have some brief patchy fog again
toward sunrise over the inland/Highway 77 corridor, but that is
about the only "notable" weather in the short term. Temperature
forecast has been based on the combination of a blend of Bias-
Consensus MOS and All grids, with some adjustments near the coast
MARINE (Tonight through Sunday night)...
Will have some elevated/moderate onshore flow tonight over the
southern bays/nearshore waters, and possibly Monday night given
the good sea-breeze which is expected tonight and continue on
Sunday night. Otherwise, weak to moderate southerly flow with no
significant weather expected.
LONG TERM (Monday through Saturday)...
Models prog a short wave to round the northwest periphery of the
ridge aloft, tapping into moisture along the Sierra Madre. However,
precip is not expected to make it into the CWA. Kept 5-10 silent
pops for a rogue tsra or two, mainly for the western areas. Models
show embedded short waves periodically through the extended, but
moisture will be very limited along with a capping inversion, thus
only went with silent 5-10 pops through Sat. A gradual warming trend
will continue through the week with highs nearing 100 degrees along
the Rio Grande by the latter part of the week. Onshore winds will
generally be weak to at times moderate through the period.
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 73 90 74 89 71 / 0 0 0 10 10
Victoria 71 92 71 91 68 / 0 10 10 10 10
Laredo 74 97 75 95 74 / 0 10 10 10 10
Alice 71 95 71 94 68 / 0 0 0 10 10
Rockport 76 88 76 86 74 / 0 10 10 10 10
Cotulla 71 96 73 95 72 / 10 10 0 10 10
Kingsville 73 94 71 93 70 / 0 0 0 10 10
Navy Corpus 78 89 78 87 76 / 10 10 0 10 10
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1151 PM EDT Sat May 12 2018
Strengthening of inflow into the mid level frontal boundary over
southern Michigan will sustain showers across the area during the
first few hours of the TAF period. Showers should end prior to
daybreak as some enhanced upper level subsidence expands across Se
Mi with expansion of thunderstorms expected to take hold just south
of the state line. With the showers, there will be some low cloud
redevelopment during the night, particularly south of FNT. As has
been the case over the last 24 hours, the circulation around the
high pressure to the north-northeast will sustain some degree of low
level dry air across the area, leading to some degree of fluctuation
in cloud heights. Current indications are that any low clouds during
the morning will lift in to a sct-bkn VFR cu field in the afternoon
with daytime heating.
For DTW...Southwest flow will force some additional
moisture/instability transport into metro Detroit early in the
morning, therefore supporting a chance for thunderstorms (primarily
in the 07Z to 10Z time frame).
.DTW THRESHOLD PROBABILITIES...
* Moderate in ceilings below 5000 ft through the TAF period.
* Moderate in thunderstorms overnight.
Issued at 839 PM EDT Sat May 12 2018
Enhanced frontal forcing along the 700-600mb front has been
supporting showers all the way up toward central Lake Mi. This
forcing will traverse Se Mi later this evening into the overnight.
Based on radar trends, an update will be issued simply to raise pops
a little higher across the northern sections of the forecast area.
Increased southwesterly flow overnight is still expected to result in
a little better convective development farther south along the
frontal slope. When this occurs, the precip farther north along mid
level front will likely wane. The latest HRRR continues to suggest
the higher intensity convection occurring later in the night
along/south of the MI/OH border, closer to better low level
convergence and instability. So the expectation continues to be that
the heaviest overnight rainfall will occur across Lenawee/Monroe
Counties and points south, south of the region which received the
heaviest rainfall earlier today.
Issued at 304 PM EDT Sat May 12 2018
Flood advisory will be allowed to expire at 330 PM as showers have
just about exited the area at press time.
Subtle upper level ridging building over the upper Mississippi River
Valley leading to northwest Confluent flow over the Central Great
Lakes, with expansive high pressure (1022-1024 MB) over Lake
Superior-Lake Huron. Low level northeast winds has subsequently
advected drier air into southeast Michigan late this afternoon, with
the 850 MB front/moisture axis now just south of the Michigan
border, with the surface boundary and instability axis well south
over the southern Ohio Valley. Surface low pressure approaching Iowa
this evening will provide the focus for yet another complex to
develop and roll east, tracking close to the southern Michigan
border tonight. It appears the low level jet will be veering quickly
to west-east direction, limiting the moisture/instability return
into the state, and still appears bulk of heavy rainfall will be
along and south of Michigan border. Still, 700 MB moisture axis/FGEN
over hanging the southern Michigan border should assure at least
some shower activity and possible thunderstorm activity south of M-
59, supported by latest HRRR. Lenawee/Monroe counties have missed
out on the heavier rain over the past 24 hours, so should be able to
handle 1+ inches ok. Obviously, if this heavier activity makes it
into Washtenaw/Wayne it will be a different story, and considered
issuing a flood watch, but was just not finding much support to get
heavier activity that far north. 12z Euro is about the only
solution, but Euro is not handling this lead wave currently over
Illinois. 12z HiRes-ARW looks like a more reasonable solution for
The frontal boundary and moisture axis will be hanging over the
northern Ohio Valley Sunday-Monday, making for a low confidence
forecast, as any ripple/wave riding along the front could lead to
shower/thunderstorm development activity toward the southern
Michigan border, despite being within the backdrop of the flat 500
MB ridge. Confidence in the temperature forecast Sunday/Monday is
also not high due to the dependence of low clouds, as NAM indicating
high degree of RH/moisture at 925 MB level through the period.
An active period of weather will continue through the extended with
a few chances for precipitation. As far as temperatures, highs are
expected to remain in the 70 degree range through the remainder of
the week and into the start of next weekend. Multiple waves will
continue to move along the flow and just to the south of the CWA.
Models are showing the best chances for rain/storms on Tuesday and
then possibly again late Thursday night into the Friday timeframe.
High pressure over the northern Great Lakes will build slowly south
into tonight, but a stalled front across the southern Great Lakes
will be slow to exit the region. The front will remain active with
showers across lake St Clair and Lake Erie through Sunday morning
before finally drifting far enough south to allow drier air to move
in. Stable boundary layer will keep wind gusts generally less than
15 knots through the next few days. The exception will be Lake Erie
where wind speeds may approach 20 knots within easterly gradient
flow around this high on Sunday.
One more round of rainfall is expected tonight as another
disturbance tracks along a nearly stationary frontal boundary. This
wave is expected to track further south and affect mainly areas from
I-94 southward. Rainfall amounts will be lighter than last night,
but still possibly range from around one quarter of an inch near the
I-94 corridor to one inch near the Michigan state line. Most
of the new rainfall will fall just south of ongoing flood issues and
should not exacerbate the situation tonight.
Issued at 301 PM EDT Sat May 12 2018
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Grand Forks ND
936 PM CDT Sat May 12 2018
Issued at 933 PM CDT Sat May 12 2018
No changes to the going forecast. Sprinkles over the southern
counties have dissipated as expected. The showers over south
central ND have been weakening as they move east and think they
will be completely gone or not reaching the ground by the time
they get into our southwestern counties. Temps have been staying
in the 50s to low 60s so far, but think as we get further past
sunset we should start dropping faster and continued to keep lows
in the 40s to upper 30s.
.SHORT TERM...(This evening through Sunday)
Issued at 305 PM CDT Sat May 12 2018
Weak high pressure exists from the Great Lakes east through
northern MN and ND this afternoon. A weakening upper level
disturbance moving thorugh SD and far southern ND may bring a few
sprinkles/light showers to far SE ND this afternoon. All in all,
not expecting much from these showers before they dissipate.
Tonight, some left over mid and high clouds will linger across the
region, helping keep temps up into the evening hours. Skies should
clear across much of the area by Sunday morning, save the south.
On Sunday, expect a westerly breeze by the afternoon...along with
dry conditions in the north. Temps should make it into the 70s
across the entire area...and maybe near 80 in the far northern Red
.LONG TERM...(Sunday night through Saturday)
Issued at 305 PM CDT Sat May 12 2018
Sunday night through Wednesday... An H5 blocking pattern sets up
firmly over the intermountain west on Sunday and produces a split
flow pattern over the Northern Plains region through the early part
of the work week. Expect generally fair and warm conditions through
Wednesday... with temperatures ranging near 10 degrees above long
term averages. Light northerly winds are expected Sunday night and
Monday... with dry, near critical, fire weather conditions likely to
persist. Tuesday will see winds swing out of the south... and with
an increasing southerly flow from Tuesday into Wednesday... humidity
levels should rise a bit.
Wednesday night through Friday... Models are consistent in showing a
breakup of the western U.S. block followed by a potentially damp
late week period... as a series of weak impulses roll across the
Northern Plains. High temperatures cool from the 70s on Thursday
into the 60s on Friday... with intermittent showers possible both
days. A predominantly southerly flow on Thursday should swap out of
the north by Friday... leading to a somewhat cooler and drier
For now... Saturday looks to end up mainly sunny and dry through the
morning, with increased clouds and a risk for showers across the
southern Red River Valley in the afternoon.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 647 PM CDT Sat May 12 2018
Conditions are VFR at all sites and will remain so throughout the
period. Light and variable winds will pick up out of the west-
southwest by late tomorrow morning, mostly staying below 12 kts.
Issued at 305 PM CDT Sat May 12 2018
Sunday afternoon is shaping up to be a near critical fire weather
day across northeast ND and northwest MN. Highs should be in the
70s to near 80 degrees. The HRRR model has done well with
humidity/dew points recently and are hinting at dew points in the
30s across the north tomorrow. The rest of the models are
forecasting more low 40 dew points. The other element of concern is
winds...which may be around 14 to 18 mph with gusts of 20 to 25
mph tomorrow afternoon. Most models don`t support anything higher
than 25 mph. However, if some areas mix all the way to 700 mb/3000
ft AGL, there could be more +25 mph gusts and will be something
for the next forecast shift to monitor/evaluate. Conditions will
improve quickly in the evening as winds decrease and humidity
Area Forecast Discussion
National Weather Service Green Bay WI
1053 PM CDT Sat May 12 2018
Updated aviation portion for 06Z TAF issuance
Issued at 840 PM CDT Sat May 12 2018
Similar scenario to Friday evening again tonight with disorganized
band of very light shower activity that had developed in weak WAA
zone north of frontal boundary over Illinois and ahead of
shortwave impulse passing across the forecast area. HRRR did a
rather lousy job capturing the shower activity earlier this but
finally seems to have handle albeit a little too late. 00Z Green
Bay sounding shows very dry air roughly below 3 km thus
precipitating cloud bases are pretty high around 7 to 9 kft. As
last evening, precipitation is again waning as it impinges on
increasingly dry air over northeast Wisconsin. Precipitation a bit
more widespread south of highway 10...but even there not much
more than a car spotter or perhaps an isolated hundredth of an
inch. Bumped up POPs for the next few hours generally south of a
GRB to ISW line to reflect current trends. After midnight mainly
mid to high clouds and dry conditions.
.SHORT TERM...Tonight and Sunday
Issued at 257 PM CDT Sat May 12 2018
An area of showers and thunderstorms should pass south of the
forecast area late this afternoon/early this evening as a mid
level short wave continues to move east and an east-west
stationary front remains across central Illinois. Mesoscale
models showed some activity to the west dissipating as it reaches
central Wisconsin. Have left some slight chance, and low end
chance, PoPs across the southern tier of counties for a few hours
during the evening to be on the safe side.
Expect mid and high clouds around for the night, but temperatures
are still likely to fall into the 30s across much of the area.
Would think frost will develop due to the light winds and chilly
temperatures. A narrow surface ridge is forecast to be over
Wisconsin on Sunday, helping to keep the area dry for at least the
daytime hours. Warmer temperatures are in store, with upper 60s
to lower 70s at most locations away from Lake Michigan.
.LONG TERM...Sunday Night Through Saturday
Issued at 257 PM CDT Sat May 12 2018
Upper flow pattern over Wisconsin will be mostly
confluent through the middle of next week, helping to keep the
Hudson Bay high to our northeast. Dry air in the low levels will
keep rain mostly to our south through midweek. An upper trough
approaching from the central Plains towards the end of the week
will help cause upper winds to back to the southwest, and some
moisture to return in the low levels from the south. So the best
chance of rain is late in the week. Temperatures will be a little
above normal for the next few days, and closer to normal later in
.AVIATION...for 06Z TAF Issuance
Issued at 1052 PM CDT Sat May 12 2018
Weak lift north of a warm front and embedded weak disturbances
aloft will continue to generate a few scattered light showers
mainly across the southern third of Wisconsin and south of the GRB
TAF sites overnight. Lower levels remain dry with cloud bases
generally above 10kft.
VFR conditions to prevail through the remainder of the TAF
period with mainly middle to high clouds traversing the area from
time to time.
Issued at 257 PM CDT Sat May 12 2018
Low relative humidities and warmer temperatures will produce
elevated fire weather conditions over central and northern WI
through the middle of next week. Sunday through Tuesday should
have temperatures in the 70s and low 80s with relative humidities
in the upper teens and 20s across northern WI. Winds are forecast
to remain pretty light through the middle of next week.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
941 PM CDT Sat May 12 2018
932 PM CDT
Showers and thunderstorms once again the primary forecast
challenge late this evening into the overnight hours. Broad
region of over-running is focused from far northwestern Iowa
across southern Wisconsin where showers and thunderstorms are
ongoing and will likely continue until after midnight tonight,
then begin to diminish in coverage as mid level southwest flow
veers to westerly. Some of these showers may dip into the northern
tier of counties in Illinois, but most will stay north of the
Farther south, modest 35-40kt speed max is located over far NE MO
per latest RAP and sampled by GOES-16 derived motion winds.
Moisture convergence on the nose of this jet is focused across
far SE IA into west central IL this evening where there has been a
modest uptick in shower coverage along with a lone isolated
thunderstorm. RAP indicates that this small speed max will weaken
beyond the next couple hours as winds begin to veer. Meanwhile,
MUCAPE of 500-1000 J/kg over the CWA should also begin to wane
after roughly midnight tonight.
Conditions seem to be peaking now and over the next couple hours
for new development so prefer to monitor upstream trends for
another hour before any more large-scale changes to the forecast.
Barring any more robust development in that time, though, and
given the expected weakening instability and forcing beyond the
next couple hours, will have to consider further reducing PoPs
and QPF along with canceling the remainder of the Flash Flood
310 PM CDT
Additional showers and storms are expected through tonight. A
stationary boundary has settled over central IL and additional
upper level waves will pass over the region. Expecting convection
to blossom over the forecast area late this afternoon, but storms
should not be severe due very little CAPE to work with. PWAT
values are 1.3-1.6 inches, so the main threat from storms will be
heavy rain. If CAPE values increase, especially south of I-80, a
couple of storms could produce large hail.
Additional showers will develop this evening with the best
coverage between I-88 and I-80. The radar estimates that up to 1.5
inches of rain has already fallen in this area, and up 2 inches is
forecast to fall through tonight. As such, issued a flash flood
watch for this corridor due to the prolonged period of
thunderstorms. Some models shift the heavy rain axis a bit further
north or south, but the operational HRRR has been very consistent
and accurate thus far today. Therefore opted to follow it`s
guidance and also focus the watch on the heavy rain core. Showers
and storms finally end from west to east Sunday morning.
105 PM CDT
Sunday through Saturday...
Main forecast concerns/challenges will continue to be with
periods of showers and thunderstorms, some of which could be
strong/severe and also be capable of producing additional heavy
At the start of the period, expected thunderstorms tonight should
be exiting to the east southeast. However, a few storms may
persist along and south of the I-80 corridor a few hours before
departing. During this time, LLJ will continue to veer though
remain on the stronger side. Also, large scale ascent with surface
reflection moving through will be in place, in the presence of
decent elevated instability. This could support a continued strong
to severe threat, with hail the main threat. Additional heavy
downpours will also be possible. By mid morning, this
precip/convection should be east of the CWA.
Guidance does vary with regards to additional shower/thunderstorm
chances for the remainder of the day Sunday. Most hires guidance
indicating a lull in the activity for much of the day, while other
pieces of guidance depict additional development along surface
boundary and reflection still in place across the southern CWA.
Can`t completely rule out additional precip chances in this
location Sunday afternoon, as it will be possible for additional
upstream mid level energy to move overhead. Given the uncertainty,
will continue going forecast of slight chance to low chance pops
mainly for locations south of I-80. With some slight warming to
the air mass along with the possibility for the sun to break out
in some locations Sunday, expect temps to be warmer than today.
Additional chances for thunderstorms remain Sunday night into
Monday morning, with another period of strong to severe storms
possible. With mid/upper level forcing supportive of steering a
stronger surface low north into the region, surface boundary will
have a chance to lift north during this time. This coinciding with
a strengthening LLJ, will once again support thunderstorm
development to our west. There is some uncertainty as to exactly
where this will initiate, along with where this will track. Some
guidance would indicate much of northern IL and northwest IN
observing these thunderstorms. However, I wonder if more southerly
track would be favored, following instability axis. If this were
to occur, then locations south of I-88 would have the highest
chances for thunderstorms. Given the change in the overall pattern
and with increasing instability, a hail and now a damaging wind
threat would be the hazards.
Similar pattern into mid week will support additional
thunderstorm chances, with similar hazards also possible. Night
time development appears to be the more favored periods, however,
day time development will also be possible.
For the 00Z TAFs...
The main forecast concerns tonight and Sunday for ORD and MDW
- Scattered showers near and north of the airports through mid-
eve, followed by a 4-6 hour period of thunderstorms at least
near the airports into the overnight
- IFR ceilings returning, likely not long after dark, and
increasing potential for LIFR ceilings (possibly down to 300 ft)
during Sunday morning
- Potential for drizzle/fog Sunday morning with visibility as low
as 3/4SM possible
In the wake of the earlier rain, IFR ceilings had developed at
Chicago area airports and have since mixed out at most. However,
these are not far away and will likely creep back in not long
after dark. In addition, scattered showers will continue in the
region early this evening.
Deeper convection is anticipated to develop across
central/eastern Iowa into northwest Illinois by mid-eve and
spread east-southeast late this eve into overnight. This looks
like a setup that will bring periodic storms for as much as six
hours to some locations of northern Illinois, and ORD and MDW are
in the favored axis. However, confidence on where exactly this
will set up and how wide of a storm axis is low-medium.
Confidence on timing is higher and this should be after peak
demand time tonight and before that of the morning.
The Sunday morning operations do look to be impacted though,
mainly by low ceilings and the potential for low visibility in
drizzle/fog. While not climatologically favored in mid-May,
northeast winds combined with the moist low levels in the wake of
the rain and increased dew points are a regime to support LIFR
ceilings. Confidence is medium in these occurring and they could
be even lower than the 500 ft presently forecast. There could be
scattered showers continuing further into the morning, and if
that were to happen, it may disrupt some of the lower ceilings at
least temporarily. Patchy drizzle certainly is a possibility too
and that would lower visibility in tandem with the lower ceilings.
Ceilings should inch their way up into the afternoon while
northeast winds remain fairly light. Showers and some storms are
likely to increase in coverage across the region later Sunday
349 PM CDT
A persistent pressure pattern will remain over the lake through
early next week. An elongated ridge from the central Plains to the
northeast will slowly shift south early next week. An elongated
trough extending from the central Plains to just north of the Ohio
River will dissipate early next week. North winds become easterly
tonight, and 10-20 kt winds are expected over the southern half
of the lake. As the ridge shifts south, light and variable winds
are expected across the lake. Winds turn southwest over the
northern end of the lake Sunday night followed by another period
of light and variable winds.
Winds become northeast across the lake as a series of surface
highs shift from Manitoba to Quebec Monday night through late
IL...Flash Flood Watch...ILZ013-ILZ014-ILZ022 until 10 AM Sunday.
Flash Flood Watch...ILZ008-ILZ010-ILZ011-ILZ012-ILZ019-ILZ020-
ILZ021 until 7 AM Sunday.
IN...Flash Flood Watch...INZ001-INZ002 until 10 AM Sunday.
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