Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/19/17
Area Forecast Discussion...CORRECTED
National Weather Service Bismarck ND
939 PM CDT Tue Jul 18 2017
.UPDATE...
Issued at 939 PM CDT Tue Jul 18 2017
Latest water vapor imagery shows multiple shortwaves across
western Idaho on the nose of a 60kt 500mb jet, continuing to ride
along the northern periphery of a broad upper level ridge. These
shortwaves and jet will reach western ND late tonight/early
Wednesday morning, followed by a more distinct 700mb-500mb
shortwave Wednesday afternoon moving across southern ND.
Soundings and latest CAM`s indicate increasing coverage of
elevated thunderstorms late tonight/early Wednesday morning as a
low level jet increases across western ND. This is then expected
to morph quickly into a large area of showers and thunderstorms
Wednesday morning, pushing quickly across central ND. Some severe
weather is possible. Another round of possible severe weather
would come in the afternoon with the aforementioned midlevel
shortwave, mainly affecting locales along and south of Interstate
94. Convection will be rather messy in the morning, and that will
play a role in how things evolve/destabilize in the afternoon,
especially if cloud cover holds in. The latest 21z SREF calibrated
severe thunderstorm has taken a noticeable uptick in the
probability of severe thunderstorms in southern ND Wednesday.
After collaborating with SPC, we will be mentioning some severe
thunderstorm wording in the gridded data and text products.
UPDATE Issued at 537 PM CDT Tue Jul 18 2017
Local/Regional radars indicative of a few supercells in southeast
Montana at this time. The experimental HRRR seems to have some
signal on what is occurring, with a couple splitting storms taking
shape as they edge closer to our southwest border. Thus far, dime
size hail being reported in southeast MT, along with gusty winds
(sub severe at this time). Mixed layer cape sufficient between
1000 and 1500 J/Kg, with strong deep layer shear between 30kt and
50kt. DCAPE/Downdraft Cape on the order of 1200 J/Kg, so isolated
damaging winds possible and will continue to monitor very closely.
Adjusted pops based on current radar, movement, and forecast into
southwest ND through 03z. Rest of forecast elements looked good.
&&
.SHORT TERM...(This evening through Wednesday)
Issued at 401 PM CDT Tue Jul 18 2017
Late this afternoon and this evening an isolated thunderstorm or
two is possible in the southwest. The SPC day 1 convective outlook
has the far southwest corner in a marginal risk for a severe
storm. The current ECMWF/GFS/RAP are indicating ample 0-6 km bulk
shear with values around 60 kts but the low/mid level lapse rates
and CAPE values are not impressive. Any chance for severe
thunderstorms in the southwest appear to be slight. The CAMS are
scattered with only the HRRR hinting at something in the southwest
around 22Z.
As we get into Wednesday, an embedded pulse in the zonal flow aloft
will result in chances for another round of showers and
thunderstorms. SPC has most of the south in a marginal risk for
severe storms. Severe weather ingredients look more promising for
storms becoming strong to severe. Additionally, the current suite
of ensemble and deterministic models are in good agreement on an
area of QPF moving from the west to southeast through the day. The
WPC day 2 QPF valid for Wednesday has between 0.10 and 0.25
inches of rain for much of western and central ND. West central
and south central areas are painted with values between 0.25 and
0.75 inches of rain. Locally higher amounts are possible with
thunderstorms.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 401 PM CDT Tue Jul 18 2017
Most of the action for the extended will come Thursday evening
through Friday, as a weak wave aloft will bring chances for showers
and thunderstorms. The SPC day 3 convective outlook has most of
western and central ND highlighted in a marginal risk for severe
thunderstorms. The 12Z ECMWF/GFS convective parameters for Thursday
are sufficient for the development of strong to severe storms.
The outlook for the rest of the long term, a chance or two for a
thunderstorm and near seasonal temperatures.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 537 PM CDT Tue Jul 18 2017
This Taf period, will be monitoring for a potential round of
showers and thunderstorms, possibly heavy and/or severe, during
the daylight hours Wednesday. Indications are that an area of
thunderstorms couple develop over eastern Montana 09z-12z
Wednesday, then quickly shift across western and central ND 12z-
21z Wednesday. Low confidence on timing and complete evolution of
thunderstorms for any one terminal. Thus for now, have not carried
any predominate mention of thunderstorms and/or intensity, but
have mentioned a vcts during the expected timeframe. Will await
the model guidance later this evening for better continuity and
confidence.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...KS/AE
SHORT TERM...AC
LONG TERM...AC
AVIATION...KS
Area Forecast Discussion
National Weather Service Cheyenne WY
414 PM MDT Tue Jul 18 2017
.SHORT TERM...(This evening through Thursday night)
Issued at 300 PM MDT Tue Jul 18 2017
Forecast challenges deal with PoPs and chances for heavy rainfall
through the short term.
Latest water vapor imagery showing a dry slot moving into most of
Wyoming this afternoon, which has really limited convection.
Exception being down in the southern Nebraska Panhandle where we
are seeing scattered convection developing. This band is moving at
a pretty good clip and should be out of the Panhandle within the
next hour or so.
For this evening, most locations to remain dry as this dry slot
remains over the area. HRRR guidance does show a cell developing
across the northern Panhandle that could impact Alliance and
Chadron. Does not look all that strong, so feel severe storms
should hold off.
PWATs on the increase for Wednesday. Counties west of Laramie
Range increase from .5" this afternoon up to .75-.8" by Wednesday
afternoon with the Panhandle increasing up to 1.3". Only trouble
for tomorrow is there seems to be no forcing mechanism as the weak
frontal boundary lifts northeast and lower elevation winds shift
southwest. So we may not see much in the way of convection outside
the mountains.
GFS and ECMWF still in good agreement for Thursday as upper high
remains well southeast of the area over eastern Kansas and
monsoonal surge moves directly over the CWFA. PWATs well over an
inch across much of the CWFA with near 1.3" in the Panhandle. Do
have an upper shortwave moving through the monsoonal flow Thursday
that should help develop convection. Greatest concentration of
showers looks to be along the I-80 corridor from maybe Sidney to
Arlington and in the mountains. HPC coordinated with us today for
a Slight Risk area for Excessive Rainfall across our south central
zones. That may need to be adjusted some more as the event draws
closer. Looks like a good bet we will need some flash flood
watches for some of our southern counties Thursday afternoon.
.LONG TERM...(Friday through Tuesday)
Issued at 300 PM MDT Tue Jul 18 2017
Friday...Relatively weak zonal flow aloft prevails. Deeper moisture
will be limited to Colorado and to areas along our Colorado state
line, thus will continue with isolated to scattered showers and
thunderstorms over and near our southern mountains, dry elsewhere.
Saturday...Drier air at low and mid levels will infiltrate our
western and central counties in the wake of a cold front. There may
be enough moisture left over our eastern counties for isolated late
day showers and thunderstorms, primarily over the Nebraska panhandle.
Sunday...The flow aloft backs to northwest with low level upslope
winds helping to generate isolated showers and thunderstorms along
our southern counties near the Colorado state line, with mostly dry
conditions elsewhere.
Monday...Low level upslope strengthens under ridging aloft. Looks
like enough low and mid level moisture over our southern and eastern
counties for isolated to scattered afternoon and evening showers and
thunderstorms.
Tuesday...Next shortwave trough aloft progged to move across during
peak heating, helping to spark scattered showers and thunderstorms
along and east of Interstate 25, and most numerous over western
Nebraska.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 412 PM MDT Tue Jul 18 2017
Wyoming TAFS...VFR, with isolated thunderstorms near Cheyenne
until 03Z. Gusts to 20 knots at Cheyenne and Rawlins after 18Z
Wednesday.
Nebraska TAFS...VFR. Gusts to 22 knots at Chadron and Sidney after
18Z Wednesday.
&&
.FIRE WEATHER...
Issued at 300 PM MDT Tue Jul 18 2017
Monsoonal moisture will remain over southeast Wyoming and
Nebraska Panhandle for the next several days into next week.
Result will be continued mountain showers and thunderstorms with a
general increase in coverage each day. Expect fairly high
afternoon humidity over the area. The exception being FWZs 301 and
303 where afternoon humidities fall into the mid teens both this
afternoon and Wednesday. Look for fair to good overnight
recoveries. Good chances for wetting rains in the mountains
through Friday with best chances Thursday, where many lower lying
areas stand to get wetting rains as well.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...GCC
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...GCC
Area Forecast Discussion
National Weather Service Flagstaff AZ
325 PM MST Tue Jul 18 2017
.SYNOPSIS...Deep moisture and an area of low pressure over
western Texas moving west will bring numerous showers and
thunderstorms to northern and central Arizona through mid-week.
Heavy rainfall from the stronger storms will be capable of producing
flash flooding at least through Wednesday evening.
&&
.DISCUSSION...Very moist atmosphere and approaching easterly waves
have produced numerous showers and thunderstorms across northern
Arizona this afternoon. Heavy to very heavy rain and over an inch
diameter hail has been observed (via radar). Very active afternoon!
Deep moisture will remain over the area through Wednesday evening.
The easterly flow across Texas and New Mexico will continue to bring
instability over Arizona. Both the HRRR and NAM show the development
of an MCS over Yavapai County or northwestern Coconino County
tonight into Wednesday.
While models have some timing and location differences concerning
the actual placement of this event all operation models are leaning
towards this solution; with the higher resolution models concurring
that a mesoscale convective system is anticipated to develop and
move across the high country in the overnight hours. Current Flash
Flood Watch is out through Wednesday evening to cover this activity.
On Thursday a slight decrease in moisture aloft is expected to move
into the area allowing for a slightly less active day for convective
thunderstorm development. Some storms are still expected to form,
however they should be more widely scatter than their counterparts
from the previous few days.
This respite will not last long with models suggesting that a
reinforcing surge of moisture will move back into the area from
the New Mexico border Friday and lasting into next week.
&&
.AVIATION...For the 00Z package...SHRA/TSRA will expand in coverage
through the afternoon with widespread coverage expected through this
evening. Storms will be moving east to west with areas of MVFR and
isolated IFR in +RA. A few storms may produce severe wind and hail
mostly south and west of a KGCN to KSOW line through around 03Z.
Expect conditions to improve from east to west aft 07Z Wed. Aviation
discussion not updated for TAF amendments.
&&
.FIRE WEATHER...Active monsoon conditions will continue with
scattered to numerous showers and storms each day. Convective
activity should continue overnight tonight as an upper level
disturbance moves through northern Arizona. The threat for heavy
rain will continue across all of Arizona through midweek. Expect
near average temperatures.
Friday through Sunday....An active monsoon pattern will continue
with daily chances for rain showers and thunderstorms. No
significant changes in the weather pattern are anticipated.
&&
.FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch through
Wednesday evening FOR AZZ004>018-037>040.
&&
$$
PUBLIC...MAS
AVIATION...MCT
FIRE WEATHER...MCT
For Northern Arizona weather information visit
weather.gov/flagstaff
Area Forecast Discussion
National Weather Service Hastings NE
742 PM CDT Tue Jul 18 2017
.SHORT TERM...(This evening through Wednesday)
Issued at 417 PM CDT Tue Jul 18 2017
The main concern for this afternoon and tonight is the potential
for thunderstorms as well as continuation of the heat advisory
this evening.
A solid layer of low to mid level cu formed late this morning and
has persisted through much of the afternoon. This has held down
temperatures across much of south central Nebraska. Highs have
struggled to get up into the upper 80s and low 90s across the area.
If this trend continues an early cancellation of the heat advisory
may be possible, although southern portions are getting closer to
criteria.
Models have not been very consistent on thunderstorm chances for
today. The NAM has kept things mainly dry for our area while the
HRRR has had a line enter from our northwest with scattered
showers and thunderstorms around through much of this evening
through tonight into the early morning hours. Although any
widespread precipitation is not expected, have kept some lower
pops across much of the area to account for lingering showers.
The best chances to see any severe weather remains across
northwestern portions of the area.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 417 PM CDT Tue Jul 18 2017
The stretch of hot weather really ramps up tomorrow through
Friday with heat indices of 100 to 108 possible across the area.
Have upgraded southeastern portions of the CWA to a heat warning
to account for heat indices near or above 105 and low temperatures
overnight only dropping to the mid 70s. Have the rest of the area
in a heat advisory for tomorrow afternoon as the prolonged nature
of the heat is a bit more uncertain in these areas, especially on
Friday with an advancing cold front expected to start moving
through the area.
The upper level flow becomes more northwesterly as we head
into the end of the week with multiple weak shortwaves providing
us with slight chances for precipitation Thursday night through
Monday. With a front expected to move through on Friday, cooler
weather is expected into the weekend with highs back in the 80s to
lower 90s.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday)
Issued at 742 PM CDT Tue Jul 18 2017
At least for now, will officially advertise a very "quiet" period
with no formal mention of thunderstorms and VFR
ceiling/visibility, although this is by no means a guarantee and
is subject to change. As for surface winds, they should be rather
light (generally 6-7kt or less) from an easterly to southeasterly
direction tonight, then picking up a bit from the south late in
the period on Wednesday afternoon with gust potential to around
18kt.
Will conclude with two of the primary/possible caveats to
the going "quiet" forecast:
1) Although the chance of thunderstorms at either site appears low
enough to no longer justify even a generic "vicinity" (VCTS)
mention, this will need closely watched, especially if any of the
ongoing activity over southwest Nebraska happens to hold together
and start propagating east.
2) There are some hints that least brief, light haze/fog (perhaps
MVFR visibility?) could materialize late tonight into Wednesday
morning. For now expect "just enough" wind/mixing to preclude
potentially more problematic visibility issues, but again, this
bears watching in later forecasts.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning from 1 PM Wednesday to 8 PM CDT Friday
for NEZ064-076-077-085>087.
Heat Advisory from 1 PM to 8 PM CDT Wednesday for NEZ039>041-
046>049-060>063-072>075-082>084.
Heat Advisory until 8 PM CDT this evening for NEZ082>087.
KS...Excessive Heat Warning from 1 PM Wednesday to 8 PM CDT Friday
for KSZ006-007-018-019.
Heat Advisory from 1 PM to 8 PM CDT Wednesday for KSZ005-017.
Heat Advisory until 8 PM CDT this evening for KSZ005>007-017>019.
&&
$$
SHORT TERM...Petr
LONG TERM...Petr
AVIATION...Pfannkuch
Area Forecast Discussion
National Weather Service Goodland KS
714 PM MDT Tue Jul 18 2017
.UPDATE...
Issued at 713 PM MDT Tue Jul 18 2017
Updated for the expiration of the heat advisory.
UPDATE Issued at 624 PM MDT Tue Jul 18 2017
Cluster of thunderstorms currently over the northwest corner of
the area. High resolution guidance having some difficulty in
capturing latest trends although they do cluster around the best
chance of thunderstorms over northern Yuma county. As a result of
the latest trends and best performing high resolution guidance, am
adjusting pops accordingly.
&&
.SHORT TERM...(This afternoon through Wednesday)
Issued at 208 PM MDT Tue Jul 18 2017
Large scale ridge extents from the southwest US, across the Central
High Plains, and into the southern Mississippi River Valley. A plume
of monsoonal moisture is shown on WV imagery to be rotating through
the western extent of this ridge and into the Central Rockies.
This afternoon-tonight: A front stalled over the Nebraska Panhandle
may shift south slightly in response to a mid level shortwave
associated with monsoonal flow riding the northern part of the ridge.
This should remain north of our CWA, but the increased forcing may
combine with weak convergence along surface trough in our northwest
to kick off thunderstorm activity. CINh has already weakened in this
region and a shallow CU field has developed. RAP analysis support ML
CAPE in excess of 2000 J/KG and PWATs around 1-1.3" range. Shear is
less impressive, so once again localized heavy rain and pulse
thunderstorms are favored (hail/wind). Thunderstorm activity is
shown by high res guidance to drift to the southeast which takes it
away from better instability, but does raise the possibility for
showers/thunderstorms further south and east than originally
anticipated. I made adjustments to account for these trends.
Wednesday: Ridge shifts just a little further north and we should
see subsidence in place and a less favorable pattern for possible
afternoon thunderstorm development. Guidance is in line with this
shift in pattern, and keeps conditions dry over our CWA.
Regarding Temperatures/Heat Advisory: We have yet to reach
advisory criteria over most locations in advised area, but it is
getting close and a few locations are just now starting to reach.
There is an upward trend in temps in line with forecast, and Tds
are remaining high in our east. No changes planned as heat index
values 103-105 (a few higher) still appear likely across advised
area. Overnight lows remain mild, but heat indices should decrease
below 75 (may be close in our far east), so a decision was made
not to extend advisory overnight. Tds may be a little lower on
Wed, but temperatures will not be much different (upper 90s/lower
100s). Result should be 103-105 heat index values confined in our
north and east, and I issued another Heat Advisory for Wed
afternoon/early evening at favored locations. I am less confidence
further west and south.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 134 PM MDT Tue Jul 18 2017
High pressure aloft is expected to move east over the plains while a
a short wave trough starts to move in behind the ridge. A few storms
are possible during the evening, mainly over the northwestern
sections of our area, due to a shift in the pattern. Thursday`s
overnight low temperatures are expected to drop into middle to upper
60s over the western half and 70-75 over the eastern half of the
forecast area.
Over the weekend, the ridge will continue to flatten out and move
towards the east on Friday. This will produce slightly cooler
temperatures over the western half of our CWA while the eastern half
is still expected to climb into the upper 90s to just over 100
degrees. A prefrontal boundary looks to push through the region from
the northwest to southeast and serve as an axis for thunderstorm
development Friday afternoon. Then a cold front will follow on
Saturday producing another chance of thunderstorms across the
region. This cold front looks to stall and weaken over the central
Plains on Sunday. This will keep showers and thunderstorms in the
forecast until the front weakens and eventually give way to another
building high pressure from the west, decreasing rain chances Sunday
night and early into Monday morning.
As high pressure returns to the region during the first part of the
week, weak troughs are expected to move through the region as well.
with that said going to keep the chance of showers and
thunderstorms that the builder is given for the end of. As for the
period. As for temperatures, expect the highs to reach into the
upper 80s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 534 PM MDT Tue Jul 18 2017
Vfr conditions are expected through the period. For Kgld, a
prefrontal trough that is currently near the site will move north
later on this evening into the overnight hours. Late tomorrow
morning the south winds will increase to near 17 knots with gusts
to near 25 knots.
For Kmck, thunderstorms will be in the area during the mid and
late evening hours. However, current trends are not matching up
well with high resolution/Cam output so have low confidence in
what will happen. This is usually happens in weak flow aloft
situations. So at this time chose to do vcts beginning at 03z and
ending at 06z. For the first half of the period the winds will be
less than 10 knots from the east or light and variable due to
thunderstorm outflow winds. By late tomorrow morning/early
tomorrow afternoon southerly winds will increase to near 15 knots
with gusts to near 23 knots.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Heat Advisory from 1 PM to 8 PM CDT Wednesday for KSZ002>004-015-
016.
CO...NONE.
NE...Heat Advisory from noon MDT /1 PM CDT/ to 7 PM MDT /8 PM CDT/
Wednesday for NEZ079>081.
&&
$$
UPDATE...BULLER
SHORT TERM...DR
LONG TERM...BW
AVIATION...BULLER
Area Forecast Discussion
National Weather Service Green Bay WI
1041 PM CDT Tue Jul 18 2017
Updated aviation portion for 06Z TAF issuance
.SYNOPSIS...
Issued at 210 PM CDT Tue Jul 18 2017
Warm and humid with periods of thunderstorms for the rest of the
work week and into the upcoming weekend.
A low amplitude band of westerlies will remain across the
northern CONUS and southern Canada into the weekend. Amplification
will begin during the weekend, and continue into next week. Though
medium range models differ on the details of the pattern during
that time, it seems likely that we`ll head back into what has
been the favored pattern during the past several weeks. That would
be a regime with a ridge over the intermountain West and a trough
over the Great Lakes.
The frontal boundary crossing the area tonight is likely to play a
major role in our weather for the next several days, as it stalls
and stretches out along the southern edge of the westerlies. At
this point it seems unlikely to move far enough south to allow for
any prolonged dry periods. The resulting numerous opportunities
for precipitation are likely to result in above (north) to much
above (south) normal precipitation amounts. Humid conditions and
temperatures near to modestly above normal are expected through
the weekend, though readings could be held back on any days with
widespread clouds and precipitation. Drier conditions and
temperatures returning close to seasonal normals are likely early
next week as the upper flow begins to tilt northwest in response
to the redevelopment of an eastern NOAM upper trough.
&&
.SHORT TERM...Tonight and Wednesday
Issued at 210 PM CDT Tue Jul 18 2017
The latest RAP analysis and satellite/radar imagery show a cold
front moving southeast from southern South Dakota to far northwest
Wisconsin early this afternoon. Showers and storms continue to
develop ahead of the front with help from a old mcv as a result from
convection over the Plains last night. The most widespread of
storms have occurred over Vilas county, and its possible that the
atmosphere may not have time to destabilize ahead of the front. The
same cannot be said for further south and east where storms have
been more isolated/short-lived and further destabilization is
expected. ML capes approaching a 1000 j/kg over central and parts
of far northeast WI where storms remain on track to develop in the
20-22z time period. 0-6km bulk shear of 25-30 kts will be sufficient
for severe storms to develop. Damaging winds and large hail remain
the primary threats through tonight.
Tonight...As the mcv exits north-central WI by early this evening, a
cold front will be moving southeast over central and northeast
Wisconsin, and clearing east-central WI by midnight or shortly
thereafter. Ahead of the front, mixed layer capes up to 1500 j/kg
will be gradually diminishing through the evening. Therefore, the
best chance of severe storms will occur for the first few hours of
the evening over the southeast half of the forecast area. Some of
the higher res models keep some precip around into the overnight
hours, so kept a small chance going, but this may be too ambitious.
High pressure will build in across northern WI in the wake of the
front late tonight. Guidance is not excited about fog chances, and
there may be just enough of a boundary layer wind to keep that from
happening. Turning cooler and less humid behind the front, with
lows ranging from the mid 50s north to mid 60s south.
Wednesday...Will likely see some morning clouds over parts of
central and east-central WI through mid-morning before drier air
arrives with the southward moving surface high. With plenty of sun
in the afternoon, raised temps a degree. Highs in the low to mid
80s.
.LONG TERM...Wednesday Night Through Tuesday
Issued at 210 PM CDT Tue Jul 18 2017
Confidence in forecast details beyond about 48 hours remains low
due to the flat upper pattern.
In addition to difficulties timing rain chances due to the low
amplitude pattern, we are having major difficulties discerning the
heavy rain/flooding potential associated with additional rounds of
convection. Several days ago, heavy rainfall and flooding seemed
like a realistic possibility given the proximity of the front.
Then there was somewhat of a model consensus to shove the front
just far enough south to keep the area safe from any flooding
rains. The overall trend during the past 24 hours was to edge
things north again, with much of the guidance suggesting a severe
MCS will roll from southeast Minnesota, across southern Wisconsin
late Wednesday night into Thursday. That may pose a risk of
damaging winds in the area (though agree with the SPC Day 2
Convective Outlook that the greatest severe threat will probably
be to our south). But at least central and east-central Wisconsin
seem likely to be affected by the northeast flank of the MCS. With
additional rain chances later this week and into the weekend, the
possibility of a flooding threat evolving across the area looks
higher than it did yesterday. Will attempt to detail the
situation along with the uncertainty in the HWO.
With little confidence in the forecast details, no significant
changes were made the forecast initialization generated from a
broad-based blend of guidance products.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 1041 PM CDT Tue Jul 18 2017
Showers and thunderstorms have ended for the most part across the
area tonight. In its wake some clearing skies and fog appears to
be forming out to the west as the skies clear. Despite little to
no fog on the MOS guidance, will put some in at the TAF sites
overnight given the upstream observations. Will hit the western
TAF sites the hardest given a sooner clearing out, with less fog
out east where skies will clear later. Once the fog clears
Wednesday morning conditions should return to VFR for the balance
of the day. Another thunderstorm complex is forecast to move in
over the western TAF sites at the end of the TAF period Wednesday
evening.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS.......Skowronski
SHORT TERM.....MPC
LONG TERM......Skowronski
AVIATION.......Kurimski
Area Forecast Discussion
National Weather Service Indianapolis IN
1003 PM EDT Tue Jul 18 2017
.UPDATE...
The Aviation and Near Term Sections have been updated below.
&&
.SYNOPSIS...
Issued at 316 PM EDT Tue Jul 18 2017
The hottest and most humid air of the year is set to expand across
the Ohio Valley and central Indiana for the second half of the week
and into the weekend. Highs in the 90s and heat indices peaking
above 100 degrees will be common. Chances for thunderstorms will
gradually increase through the next several days as well...peaking
over the weekend and into early next week. Cooler temperatures will
arrive by early next week as well as the heat is shoved off to the
south and west.
&&
.NEAR TERM /Rest of Tonight/...
Issued at 1003 PM EDT Tue Jul 18 2017
For the update...while subsidence is in place over the forecast
area, a line of strong thunderstorms moving east across Illinois is
causing some concern that ridging will not be strong enough to keep
the western counties completely dry through the night as this
complex approaches. HRRR and RAP have been trending in this
direction for the last few runs, and while the system will have
trouble maintaining itself the further east it comes, it may have
just enough moisture and dynamics to keep from dissipating until
after a shower or storm have moved into the northwestern counties.
Given the strength of the subsidence only low confidence that this
will occur, but enough of a chance that it deserves a slight chance
mention starting at 9z. At this time will not add anything to the
Wednesday morning (after 12z) portion of the forecast but rather
continue to monitor how the system develops over the next several
hours. Maintained mention of patchy fog with moist boundary layer,
but lower confidence in this outcome especially west and northwest
because of potential influence of mixing from aforementioned
showers/storms. Going low temperatures in the upper 60s to low 70s
look on track with current temperatures at 10 pm mainly in the low
to mid 70s and dew points in the upper 60s. Relevant parts
of previous discussion follow...
Capping will become more prevalent across the entire forecast area
this evening into the overnight with deeper subsidence overspreading
the region under an expanding ridge aloft. Skies will become mostly
clear tonight and with light flow and lingering low level
moisture...anticipate patchy fog development once again in the
predawn hours through daybreak Wednesday. Should see dewpoints fall
back just a bit from current readings with the drier air aloft being
drawn to the surface which will limit the humidity a bit.
Temps...very likely looking at the last night with much of the area
falling into the upper 60s until late weekend at the earliest. As
mentioned above...a slight lowering of the dewpoints will take the
edge off the mugginess tonight. Frankly tonight will feel pleasant
compared to what is coming the next several days.
&&
.SHORT TERM /Wednesday through Friday/...
Issued at 316 PM EDT Tue Jul 18 2017
Forecast challenges focus first and foremost on heat and humidity
expectations with the expanding heat ridge and the potential for
parts of the forecast area to be impacted by the convective clusters
that will ride around the periphery of the ridge.
The growing heat ridge centered over the High Plains this afternoon
will gradually shift E/SE through the short term...eventually
centering over the Tennessee Valley by the beginning of the weekend.
The position of the center of the ridge and expectation for mid
level heights at 592-594dm to make it into central Indiana by
Thursday and Friday support the likelihood of the hottest
temperatures experienced yet this year to pay a visit to the region.
Expectation for dewpoints remaining in the mid and even upper 70s at
times by Thursday and Friday ensure oppressive levels of humidity
and combined with the forecast temperatures...max heat indices
rising to 100 to 105 degrees for much of the area by Thursday and
Friday. It remains a bit premature to introduce any sort of
headlines for the expected heat with the main impacts still at 36
hours away at earliest. The potential for a heat advisory is growing
and will eventually need to be considered...especially over western/
southwestern parts of central Indiana. At this time...will continue
to highlight heat stress dangers via the HWO and social media
platforms.
The other significant issue to consider in the short term is the
potential for convection to impact parts of central Indiana...
primarily from convective clusters riding through the northwest flow
along the periphery of the ridge. While model guidance remains
focused on the main path of storm cluster staying largely to our
north from the upper Midwest southeast through the lower Great
Lakes...cannot stress enough that if the mid level heights and ridge
expansion are any weaker than currently progged...a greater
potential would develop for these clusters to drift further south
and impact parts of central Indiana. Taking that possibility into
consideration will continue to keep a low chance pops running
through the period...focused over the northern counties and during
the afternoon and evenings. Additionally with so much moisture
present in the low levels...cannot entirely rule out a stray shower
or storm during peak heating any of the afternoons although presence
of a modest cap should keep that largely at bay.
As we experienced over the last few weeks...each convective clusters
will have the potential to produce all forms of severe weather with
damaging winds serving as the main threat. Heavy rain and flooding
will also be possible with every cluster considering the high PWATs
present. As it stands at this point...the northeast quadrant of the
forecast area is likely most susceptible to be impacted by the
southern fringes of a convective cluster with little to no threat
for storms expected over the southwest counties in closer proximity
to the core of the ridge aloft.
Temps...after a day with upper 80s and low 90s Wednesday...the bulk
of the hottest weather comes Thursday and Friday as 850mb temps
surge above 21-22C and the highest mid level heights are realized.
Taking this at face value...mid 90s could be argued for much of the
area. However...there are a few reasons why think the only part of
central Indiana that has a shot at the mid 90s either Thursday or
Friday will be the lower Wabash Valley and areas predominantly
southwest of a Terre Haute-Bedford line. These areas have been drier
over the last 4-6 weeks and are much closer to the core of the
ridge. Further northeast across the rest of the forecast area...the
combination of high soil moisture content courtesy of all the recent
rains and the high dewpoint air will limit full warming.
Additionally...both afternoons the mixing level maxes out at only
4kft or so. Would really like to see that at 5-6kft to be able to
tap into deeper warming. Right now...see Indy getting as warm as 92-
93 Thursday and Friday. Relief will be hard to come by at night as
lows settle in the mid 70s in the muggy airmass.
Forecast confidence is medium to high regarding the heat and
humidity...and low with respect to thunderstorm timing...coverage
and location of impacts.
&&
.LONG TERM /Friday Night through Tuesday/...
Issued at 236 PM EDT Tue Jul 18 2017
The long term period will be characterized by near constant low to
middling chances for thunderstorms much of the area, and heat
gradually returning closer to more seasonal levels, while humidity
remains relatively high until late in the period.
Large scale pattern will feature near zonal flow early in the period
with the main storm track potentially in or near the area.
As the period wears on, the ridge will again strengthen over the
western US, allowing larger scale troughing to move into the Great
Lakes. This will keep storm chances going across the area.
As usual, the near constant storm chances are largely a result of
significant uncertainty with respect to mesoscale evolution on
longer time scales, and there will likely be lengthy periods of dry
weather punctuated by multiple rounds of thunderstorm complexes.
&&
.AVIATION /Discussion for 190300z TAF issuance/...
Issued at 1003 PM EDT Tue Jul 18 2017
Updating current conditions only. May need to address line of storms
moving east across Illinois for potential impact to KLAF, but at
this point very low confidence that these will reach and directly
impact KLAF so will leave out at this time. Previous discussion
follows...
Light winds and humid airmass will lead to fog development
overnight. High confidence that at least some patchy fog will form
at the sites starting around 7-9z, but low confidence on how low the
visibilities will get. Will go with prevailing MVFR and tempo IFR
until around 12-13z. The western sites have seen more subsidence and
less cloud development during the day so may leave IFR out there or
shorten the length of time. Will go most pessimistic at KBMG. After
around 12-13z should see any visibility restrictions clear and then
VFR for the rest of Wednesday.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...Ryan
NEAR TERM...Ryan/CP
SHORT TERM...Ryan
LONG TERM...NIELD
AVIATION...CP
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
927 PM CDT Tue Jul 18 2017
.UPDATE...
Issued at 914 PM CDT Tue Jul 18 2017
Thunderstorms are staying just northeast and south of the area at
mid-evening. Still expect the rest of the night to remain dry as
RAP is showing little forcing for showers and thunderstorms over
the area overnight. Temperatures have slowly dropped the past few
hours are now mainly in the 70s and lower 80s except in metro St.
Louis where is still in the mid-upper 80s. Going lows still look
good for now.
Britt
&&
.SHORT TERM... (Through Late Wednesday Afternoon)
Issued at 255 PM CDT Tue Jul 18 2017
The synoptic pattern early this afternoon features a strong upper-
level ridge anchored across the central Plains. This ridge will
slowly meander eastward through the period, enhancing its influence
over the Midwest which will help bring even warmer temperatures to
the region on Wednesday.
Main forecast concern will be the dangerous heat which has started
across the area today and will only worsen on Wednesday. Latest air
temperatures this hour sit in the low to mid 90s (STL at 97) which
coupled with dewpoints in the upper 60s/70s have yielded heat index
values from 95-105. As we head into Wednesday, the upper-level
ridge building overhead should help push a weak boundary off to the
northeast of the region. The further northward displacement of the
front should enable dewpoints to mix out more efficiently than they
have today. That being said, increasing 850mb temps and 1000-850mb
thicknesses suggest temperatures will likely be warmer than today,
with values in the mid 90s and into the 100s in the STL metro. This
will translate to heat index values topping out near 105 in many
areas (especially along/north of I-70). Given the heat is only
expected to worsen Thursday into the upcoming weekend (see long term
section below), have decided to upgrade portions of the Excessive
Heat Watch to an Excessive Heat Warning in all areas but southeast
MO and extreme southwest IL. In these areas, slightly lower
dewpoints should limit heat index values to the 100-104 range.
The other more minor forecast concern will be on convective chances
this afternoon into this evening. Latest radar imagery depicts some
very isolated showers along a weak front over southeast MO and along
a differential heating zone over central MO. Given a fairly uncapped
atmosphere, we will likely continue to see isolated shower/storm
development in these regions through early this evening. Will have
to keep an eye on an MCV/compact shortwave trough diving through the
weak northwest flow aloft this evening. This mid-level forcing has
been enough to force some showers and isolated storms over northwest
MO, which could move into northeast MO and west-central IL through 2-
3Z (perhaps even lingering a bit later). Guidance has not handled
this system well today so confidence in convective coverage
associated with this feature is fairly low.
KD
.LONG TERM... (Wednesday Night through Next Tuesday)
Issued at 255 PM CDT Tue Jul 18 2017
A widespread and significant heat wave will be ongoing at the start
of the period with a strong upper level RIDGE dominating our region.
Although the strength of this RIDGE will weaken some heading into
Friday and Saturday, it is enough to maintain the going pattern and
effects thru this time period, as it will have the effect of hanging
a surface cold front to our north with southwest surface flow over
our region and minimal chances for rain. Look for max air temps
from the the mid 90s to the low 100s with heat index values from 105
to 114 each afternoon and early evening. The remnant Heat Watch
will be converted to a Warning for all areas outside of southeast MO
and far southern IL, with those areas being converted to an Advisory
where the cooler effects of the Ozarks will place peak heat indices
a bit more in check.
All of the models develop, at some point, increasing NW flow aloft
in response to a TROF settling into the Great Lakes region with this
to continue into early next week. The point of contention remains
just exactly when do they do it, which will directly impact on when
this current heat wave ends. The GFS continues to suggest the need
for an extension of heat headlines for many areas into Sunday, while
the CMC and to a slightly lesser extent, the EC are showing much
less of a need, especially in the northern CWA. We currently have a
Heat Watch for our southeast MO and far southern IL counties thru
early Sunday evening and this remains a plausible and valid time for
that area given a decent consensus that the front will remain
upstream. All other areas further north, the uncertainty increases
and decided to keep the end of the heat headlines at early Saturday
evening for now until we get a better handle on timing of the late
weekend cold front.
Models then come into better alignment by Monday, with NW flow aloft
and a cold front thru and bring to an end this latest heat event
with more seasonable temps, if not a little below average. What
looks to be more dubious is the pcpn chances, and prefer to keep
that at or below CLIMO values for now.
TES
&&
.AVIATION... (For the 00z TAFs through 00z Wednesday Evening)
Issued at 619 PM CDT Tue Jul 18 2017
Isolated thunderstorm near Quincy is expected to move east of the
terminal by 00Z. Otherwise, mainly dry and VFR conditions are
expected through the period has a surface high currently over
Illinois moves off to the east. Winds will remain light.
SPECIFICS FOR KSTL:
Dry and VFR conditions are expected through the period with light
winds.
Britt
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon Wednesday to 8 PM CDT Sunday for
Crawford MO-Iron MO-Madison MO-Reynolds MO-Saint Francois
MO-Sainte Genevieve MO-Washington MO.
Excessive Heat Warning until 8 PM CDT Saturday for Audrain MO-
Boone MO-Callaway MO-Cole MO-Franklin MO-Gasconade MO-
Jefferson MO-Lincoln MO-Marion MO-Moniteau MO-Monroe MO-
Montgomery MO-Osage MO-Pike MO-Ralls MO-Saint Charles MO-
Saint Louis City MO-Saint Louis MO-Shelby MO-Warren MO.
Excessive Heat Warning from noon Wednesday to 8 PM CDT Saturday
for Knox MO-Lewis MO.
IL...Heat Advisory from noon Wednesday to 8 PM CDT Sunday for
Randolph IL.
Excessive Heat Warning until 8 PM CDT Saturday for Madison IL-
Monroe IL-Saint Clair IL.
Excessive Heat Warning from noon Wednesday to 8 PM CDT Saturday
for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette
IL-Greene IL-Jersey IL-Macoupin IL-Marion IL-Montgomery IL-
Pike IL-Washington IL.
&&
$$
WFO LSX
Area Forecast Discussion
National Weather Service Nashville TN
733 PM CDT Tue Jul 18 2017
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
Radar this evening continues to show a few scattered showers and
thunderstorms in far northwest zones as well as in far southeast
zones. With loss of daytime heating underway, this activity should
quickly diminish over the next couple of hours as HRRR also
suggests. Will keep in a slight chance pop over northwest and
southeast zones to account for this activity as well as adjust sky
cover. Otherwise, forecast is on track with another warm humid
night expected.
&&
.AVIATION...
00Z TAF DISCUSSION.
VFR. A few models are indicating potential for fog overnight,
especially for KCKV and KCSV, but majority showing VFR conditions
to prevail. Winds will be light and variable through mid morning
before becoming more northerly/northwesterly for the late morning
through the afternoon hours.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION......Shamburger
AVIATION........Barnwell
Area Forecast Discussion
National Weather Service Las Vegas NV
709 PM PDT Tue Jul 18 2017
.SYNOPSIS...A moist and unstable airmass will result in scattered to
numerous thunderstorms and locally heavy rainfall across southern
Nevada...Northwest Arizona...and far eastern California through the
week. Drier conditions are expected across most of Inyo county where
temperatures will remain hot and skies mostly sunny. A slight drying
trend is possible by the end of the week.
&&
.NEAR TERM...Current area of interest is small cluster of
thunderstorms over eastern San Bernardino County...basically bounded
by Nevada Highway 163 to the north...Highway 95 to the east and
Interstate 40 to the south. Believe this area will continue to slowly
build southward this evening so decided to expand the Flash Flood
Watch to include eastern San Bernardino County and far southern
Clark County. Earlier storms over the Lake Mead Natl Rec Area and
Mohave County have dissipated for the time being. Cluster of storm
moving west near Wickenburg AZ look as they will stay south of
Mohave County/San Bernardino County. Secondary line of storms
further east in Arizona could effect Mohave County later this
evening/overnight and eventually Clark County around daybreak
Wednesday. There is still quite a bit of uncertainty in this
scenario as the HRRR has not been the most consistent today in its
simulations.
&&
.PREV DISCUSSION...239 PM PDT Tue Jul 18 2017
.DISCUSSION...High pressure over the southern U.S. will be the
dominant feature at least through Saturday. This will keep east to
southeast flow over our area, keeping the door open for monsoon
moisture in much of the area, with the possible exception of the
northwest corner of the area where drier southwest flow prevails.
Precipitable water of 1.5 to 2 inches was present over the Flash
Flood Watch area this afternoon. Storms were already beginning to
pop over Mohave County, and more significant storms over Coconino
and Yavapai Counties should roll west into Mohave County later in
the evening due to easterly steering flow. Thus, the watch looks
good, and made no changes to it. Day to day precip variations
through the week will partly be driven by the previous day`s
thunderstorm activity, which will stabilize the areas where it
occurs, push moisture and outflow boundaries into nearby areas to
help fuel storms the next day, and also leave differential heating
boundaries around the edges of both the cloud shields and the rain
footprints. Thus, made no significant changes to precip forecasts
beyond Wednesday. Nudged temperatures up a bit the next two days as
confidence has decreased in the idea of widespread cloud cover
inhibiting heating.
&&
.AVIATION...For McCarran...Through the rest of this afternoon and
into the evening, there will be an increased chance of thunderstorm
activity in and around the Las Vegas valley. Storms are likely to
form along the higher terrain and are especially likely to form
along the McCullough Range this afternoon and evening. Any storms
that form in the valley or drift into the valley will likely bring
variable erratic and gusty winds and lower visibilities. These
conditions will likely be relatively short in duration. Besides
thunderstorm influences, winds should be southerly varying from 150-
220 until diurnal southwest to westerly winds kick in overnight. SCT
to BKN above 10 kft with occasional MVFR conditions with
thunderstorm activity.
For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered thunderstorms expected across most of Mohave,
portions of Clark, Lincoln, and portions of southwest San Bernardino
counties this afternoon through the forecast period. Any storms that
form will cause variable erratic and gusty winds with low ceilings.
Otherwise winds should be southerly and diurnal with ceilings above
10 kft.
&&
.HYDROLOGY...Creeks, streams and rivers in northern Inyo County
continue to run high and fast from snow melt. Some road closures
continue in the area. Bishop Creek Bypass and Big Pine Creek Bypass
continue to be utilized to minimize flows through Bishop and Big
Pine. Isolated thunderstorms over the mountains may aid snowmelt
runoff and keep some drainages elevated over the coming days as
well. Remember, never drive through flooded roadways or around
barricades. Also, pastureland or farmland adjacent to creeks,
streams or rivers could experience areas of standing water.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
Update...Pierce
Morgan/Kryston
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