Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 06/18/18
Area Forecast Discussion
National Weather Service Burlington VT
1039 PM EDT Sun Jun 17 2018
An active weather day is anticipated on Monday with several
rounds of strong to severe convection, along with very warm and
humid conditions. Temperatures are expected to reach the mid to
upper 80s with localized valley locations near 90, combined with
humidity values will create heat index values well into the 90s
on Monday. Thunderstorms will be capable of producing very heavy
downpours with potential for isolated flash flooding, gusty
winds, and frequent lightning. The thunderstorm threat will end
by late evening on Monday with much cooler and drier air
arriving on Tuesday.
.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 1033 PM EDT Sunday...Late this evening, GOES-16 IR imagery
continue to indicate abundant cirrus/cirrostratus settling NW-
SE across the North Country in anticyclonically curved flow
aloft. This will help mitigate radiative cooling effects,
keeping overnight lows in the mid 60s to lower 70s (warmest in
the Champlain Valley). Dewpoints haven`t risen much yet, and
won`t until after sunrise Monday. Looking at 2-m dewpoints
ranging from the mid-upr 40s across VT, to the lower 60s across
the St. Lawrence Valley, with continued S-SW flow expected
There are some modest 700-500mb height falls overnight, and
this will allow for some possible light rain showers along the
Intl Border. Maintained 20-40 PoPs for nrn counties thru 12Z
Previous Discussion...Water vapor shows mid/upper level ridge
axis across the mid Atlantic/eastern Great Lakes with fast
westerly flow aloft with embedded s/w`s and ribbons of moisture
on northern periphery of ridge. For tonight, watching cluster of
storms over the northern Great Lakes which are progged to move
quickly in the western flow aloft over southern Canada. Latest
guidance continues to support threat of showers with embedded
rumbles of thunder, near the international border aft midnight
tonight. RAP shows sfc based cape values of 400 to 800 j/kg,
along with weak ribbon of mid level moisture and enhanced lift
couplet impacting our northern cwa with embedded s/w energy.
Given time frame and moving into subsidence from ridging, would
anticipate a decaying mcs with area of rain and embedded
lightning. Temps with mid/upper level debris clouds, increasing
sfc dwpts, and southerly winds will be very mild tonight.
Thinking mid/upper 60s mountains to lower 70s slv/cpv with a
muggy feel to the airmass.
Monday/Monday Night...An active period of weather is anticipated
with several rounds of strong to severe thunderstorms with localized
heavy rainfall and gusty winds, along with very warm/humid
conditions. We are thinking several rounds of convection is likely
with first associated with pre-frontal trof/terrain induced btwn 16-
20z. Latest NAM3/BTV 4km and NSSL WRF develop sfc based instability
values of 1800 to 2200 j/kg by 16z with a ribbon of enhanced 850 to
700mb winds of 40 to 50 knots, creating 0 to 6 km shear values of 35
to 45 knots. The limited factor will be the lack of significant
synoptic scale forcing/convergence so anticipating scattered to
numerous pulse type storms with isolated severe likely given
instability. The primary threat would be localized damaging wind
gusts, but given EL>40 kft and large CAPE profiles a few
stronger updrafts will be capable of producing 1 inch hail, even
with high WBZ/Freezing levels. SPC has upgraded our day2 outlook
to place our entire cwa in slight risk. Given the warm cloud
depths>12kft and pw`s between 2.0 and 2.25 very high rainfall
rates of 1.0 to 1.5 inches per hour are likely. Storm motion
vectors show individual storms moving from west to east, with
some potential for back building given the low level jet
orientation. Feeling is the first round the threat for flash
flooding will be limited, but set the stage for additional
threat as line of storms develop during the late aftn/early
Additional thunderstorms are anticipated btwn 21z and 01z associated
with cold front and better short wave energy. However, the
uncertainty will be amount of clearing/sfc heating from earlier
convection and how much instability can develop before fropa.
Current guidance suggests sfc based CAPE values will recover between
1500-1800 j/kg with 0 to 6 km shear values of 35 to 45 knots to
support a broken line of strong to severe thunderstorms. Given the
wind profiles and thermal dynamics, thinking strong/gusty winds will
be primary severe threat with isolated to scattered power
outages/trees down possible. Storm vector analysis show individual
cells moving west to east at 25 to 30 mph, as entire line of storms
tracks slowly from nw to se across our cwa. Given the 925mb to 850mb
jet of 35 to 40 knots, paralleling approaching boundary, some
potential for back building/training convection exists, which may
create isolated flash flooding. Pw`s remain near climo max for the
date, with values btwn 2.0 and 2.25 with enhanced pooling ahead of
approaching boundary. This supports the idea of additional very
heavy rainfall rates with a greater potential for isolated flash
flooding, especially over areas that receive earlier rainfall from
pre-frontal trof. Its been noted the differences in instability
between the gfs and wrf models is from wrf`s showing sfc dwpts in
the mid 70s, resulting in higher cape values, while gfs shows sfc/2m
temps only in the upper 70s to mid 80s, resulting in less cape.
Taking an average shows values between 1500 and 2000 j/kg with
Next concern is heat index values for Monday, as temperatures reach
the mid 80s to lower 90s with dewpoints approaching 70f. 925mb temps
are 1 to 3 degrees warmer on Monday with values near 24c, but
expecting more clouds/storms and less mixing due to saturated
column. These high temps with expected dwpt values create max heat
index readings mainly btwn 90 and 95 degrees btwn 11 AM and 2 PM on
Monday, with warmest values of 95 to 98 in the urban areas of
the southern CPV and lower ct river valley. Therefore will issue
heat advisory for Eastern Essex NY, Western
Addison/Rutland/Chittenden and Windsor counties in VT. Further
north the uncertainty on clouds and impacts on temps, along with
only a few isolated areas touching 95f for an hour, have held
off on issuing heat advisory.
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 342 AM EDT Sunday...By Tuesday morning, the front will
have pushed through the forecast area and surface high pressure
centered over southern Ontario will build in to the North
Country. The arrival of drier air behind the front will bring a
return to more seasonal weather with highs in the 70s Tuesday
and a noticeable decrease in the "mugginess". Should see plenty
of sunshine during the day, and mostly clear skies overnight
will allow nighttime lows to cool to the lower to mid 50s in
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 342 AM EDT Sunday...The long term forecast looks fairly
benign overall with no major features progged to move through
New England through the end of the work week. A broad trough
will remain over eastern Canada, with multiple embedded shortwaves
moving through and attempting to amplify the upper-level
pattern. The net result of this will be persistent dry,
seasonally warm northwesterly flow with some mild cool downs as
shortwaves bring shots of cooler air southeastward. High temperatures
will stay in the low 70s to low 80s range Wednesday through
Friday, and the dry air mass in place will allow lows to reach
the 40s to low 50s each night. For now have included VCSH
instead of prevailing rain and thunderstorms, just want to see
how things begin to develop tomorrow first.
Overall fairly high confidence in the larger scale pattern
through Friday, but uncertainty starts to arise looking into
next weekend as models struggle to handle the evolution of the
upper level pattern. Initial indications look to trend warmer
and more humid going into the weekend, with the potential for
increasingly active weather Sunday/Monday.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Through 00Z Tuesday...High clouds streaming over the area this
afternoon will thicken and lower through the overnight hours as
an increasingly moist, unstable air mass moves in. A cluster of
storms over the northern Great Lakes area will approach the
forecast area overnight as it moves eastward, but expecting this
system to skirt just to our north. After 12Z, increasing
instability will lead to pop up showers developing, particularly
over mountainous terrain. Between 15Z and 18Z, expect coverage
of showers to increase some, particularly in northern areas of
the forecast area. The better chances of more widespread,
organized convection will be after 18Z tomorrow, but some areas
could see some showers with heavy rain before 18Z. Visibilities
will be reduced in heavy showers, but expecting ceilings to
remain above 5000 ft.
Southerly/southwesterly winds under 10 kts will ramp up to 10 -
15 kts after 12Z, with some gusty winds possible in any storms
that develop. Could also encounter some areas of turbulence
tomorrow due to the thunderstorms, particularly in and around
Monday Night: VFR. Chance SHRA, Slight chance TSRA.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. NO SIG WX.
Wednesday Night: VFR. Slight chance SHRA.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.
Scattered to numerous showers and thunderstorms are expected to
develop midday Monday and continue into Monday evening. The
combination of precipitable water values of 2.0 to 2.25 inches
and storm motions supporting some training of convection,
supports the threat for isolated flash flooding. Given the
available moisture in the atmosphere, any storms will be capable
of very heavy rainfall rates of 1 to 1.5 inches in an hour,
which over terrain or urban areas could cause isolated flash
flooding. Given the very recent dry weather widespread/large
stem river flooding is not anticipated, but sharp rises on
smaller streams in complex terrain where multiple rounds of
storms occur is possible.
VT...Heat Advisory from 11 AM to 6 PM EDT Monday for VTZ005-009-011-
NY...Heat Advisory from 11 AM to 6 PM EDT Monday for NYZ035.
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
953 PM EDT Sun Jun 17 2018
Hot high pressure will build atop the region through the middle of
the week. Scattered afternoon and evening thunderstorms are expected
each day, focusing over the mountains. Moisture will increase
towards the end of next week as a weak frontal boundary sags toward
.NEAR TERM /THROUGH MONDAY/...
As of 945 PM EDT Sunday: Some minor tweaks to hourly trends but
otherwise no significant changes for the late evening update.
Otherwise, high pressure will dominate the weather for the near term
and beyond with a Bermuda high off the coast and an upper ridge over
the Eastern CONUS. The only change for the next 24 hours will be an
increase in the strength of a surface trough east of the
Appalachians that modifies the otherwise broad area of high pressure
over the SE CONUS. This weak trough will modify surface wind
direction, but do little else, with winds remaining light and
somewhat variable. Moisture and unseasonably warm to hot afternoon
temperatures will continue with heat indexes reaching the mid to
upper 90s this afternoon and on Monday. Warm temperatures aloft
will limit CAPE development in the afternoons, and some increase in
the strength of the capping inversion is also anticipated. This
will limit intensity of thunderstorm activity and confine initiation
to the mountains. Any storms that do develop have the potential for
brief low-end severe wind gusts. CAMs mostly have convective
showers confined to the mountains, with the HRRR having a couple
spots of convection in piedmont areas with weak updrafts. Have,
thus, de-emphasized thunderstorms in piedmont areas this afternoon
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 215 PM Sunday: Strong upper ridging will remain in place
across the western Carolinas and northeast Georgia through Tuesday.
Winds will be very light up the column and this minimal steering
flow should keep convection mainly over mountain sections, where
slow-movers will create an isolated heavy rainfall threat with any
downpours that develop. Additional triggering will be possible east
of the mountains in weak lee trough convergence, but coverage will
be more isolated in nature there. Very warm mid-level temps should
keep severe weather to a minimum. Expect plenty of 100 to 104 heat
index values east of the mountains, and a few piedmont locations
could flirt with 105 if dewpoints do not mix sufficiently.
Height falls across the northern tier will improve the westerlies
slightly over the region on Wednesday. Weak vorticity lobes riding
over the southeast ridge could aid diurnal triggering Wednesday
afternoon, but continued warm mid-level profiles will inhibit most
of the severe potential. Westerly downsloping will improve warming
east of the mountains, and there could be slightly better dewpoint
pooling south of the frontal boundary through the Virginias late
Wednesday. Expect another afternoon of heat index values rising into
the 100 to 105 range. The HWO mention will continue even though Heat
Advisories are currently looking a bit marginal.
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 200 PM EDT Sunday: The medium range remains dominated by hot
and humid conditions and a diurnal pattern of showers and
thunderstorms each day. By the time the extended period picks up 00Z
Thursday, the strong upper ridging over the SE CONUS will be in the
process of waning while a large upper trough digs into the eastern
CONUS. A frontal boundary will slowly sag southward as this trough
descends, finally making it into our area by Friday. Some moisture
will accompany the boundary, which will serve as a focus for diurnal
convection, especially Friday and Saturday. Guidance then suggests
that an upper low/trough will swing into the central Plains and
drive another frontal boundary towards the area over the weekend.
This should enhance the pattern of diurnal showers and
thunderstorms, increasing not only the likelihood but also the
coverage through the end of the week and into the weekend.
Temperatures will remain hot on Thursday with dew point likely only
mixing out to the highs 60s at best in the afternoon hours, meaning
another day of heat indices flirting with advisory criteria. Heights
will fall just enough on Friday through the weekend for max temps to
drop to within 5 degrees of normal. Min temps will remain above
average through the period.
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: No changes for the KCLT TAF for the 02z AMD.
VFR through the period, except for mountain valley fog expected
again in the morning and low VFR fog also possible at
KAVL/KAND/KHKY. Another round of mainly mountain convection expected
Monday afternoon/evening and have introduced PROB30 for KAVL. Winds
generally SW 5kt or less through the period.
Outlook: Typical summertime potential for diurnally-driven showers
and thunderstorms will persist into midweek, thanks to a large upper
level ridge, bringing hot and humid conditions. Some morning fog will
also be possible in the mountain valleys and over lakes each day.
Chances for precip look greater late in the week as the ridge begins
to break down.
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 83% High 100% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU High 100% High 100% High 100% High 100%
KAND High 100% High 100% High 100% High 100%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
Area Forecast Discussion
National Weather Service Jacksonville FL
713 PM EDT Sun Jun 17 2018
.UPDATE...Radar shows scattered convection which should
gradually diminish. May see some flare up with converging
outflow boundaries Suwanne Co to Baker Co. for an hour or two.
Otherwise...partly cloudy skies Tonight with low temps near our
current forecast lows. Latest hi-res guidance not showing much
precip after midnight thru mid-morning Monday...so made some
adjustments to hourly POP/weather grids for this period.
.AVIATION...VFR conditions through Tonight. Latest HRRR suggests
some lower clouds possible around coastal TAF sites...but SREF
not showing this. Put in a 4hr TEMPO for MVFR CIGS 10z-14z at
KSSI and KSGJ for now. Limited VCTS tomorrow to just KVQQ and
KGNV with minimal TSRA coverage anticipated at TAF sites further
.MARINE...No significant changes planned for next CWF issuance.
High pressure to the north will continue the east to southeast
winds through Monday. Surface ridge pushes south of the area by
midweek resulting in an offshore flow pattern again interrupted
by daily seabreezes. Low wind speeds and sea heights are expected
over the next few days.
Rip Currents: Moderate risk on Monday with onshore winds.
.PRELIMINARY POINT TEMPS/POPS...
AMG 71 91 71 92 / 20 50 20 40
SSI 76 86 75 89 / 10 20 10 20
JAX 73 90 72 92 / 10 20 10 40
SGJ 75 87 72 89 / 10 20 0 30
GNV 72 91 71 92 / 30 40 20 40
OCF 72 92 71 92 / 30 30 20 30
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
805 PM CDT Sun Jun 17 2018
804 PM CDT
Quiet but humid, warm evening across the CWA. Rain-cooled outflows
from earlier did push some temperatures down (e.g. 82 in Morris),
but also nudged up dew points in these areas. Can`t rule out some
shallow fog in these areas overnight if it clears of cirrus. As
for the prolonged effects of the heat, the urban heat island of
Chicago and adjacent suburbs are doing well to retain the heat,
with downtown, O`Hare, and Midway all at 88 degrees as of 8 pm.
Early evening satellite imagery and 00Z upper air raobs indicate a
series of short waves from the central Plains into northern
Wisconsin with multiple areas of convection. One wave with a 1007
mb surface low is moving eastward in northern Wisconsin, and
convection ahead of this has shown some cold pool push. Corfidi
vectors for this activity are oriented more south-southeast, and
there continues to be good surface and low-level moist flow into
this so expecting to see that trend gradually play out. Some of
this convection itself, or isolated convection developing ahead of
this on outflow, could reach southeast Wisconsin after midnight.
In addition, more convective activity favored across the
Minnesota/Iowa border region late this evening could also advance
into southern Wisconsin late tonight per analysis and support of
convective-allowing models. This poses some concern for at the
least outflow reaching into northern Illinois including Chicago
into Monday morning, and even the possibility to bubble isolated
storms. For now have just slightly expanded southward the early
morning slight chance of storms, as confidence on this is low,
but would at least expect some convective activity late
tonight/very early tomorrow morning in southern Wisconsin.
Forecast for Monday continues to look in good shape with the
points noted in below AFD. Concerns for heavy rain potential
Monday evening into the overnight are certainly there with 00Z
raobs at MPX and OAX indicating over two inches of precipitable
water, and a potential for west-to-east training setup with
generally light propagating vectors off that development corridor.
Uncertainties remain on just how quickly the frontal and post-
frontal convection work their way into the CWA from the north on
Monday evening, as well as some potential for pre-development with
RAP soundings for tomorrow afternoon indicating the cap likely
being close to being breached.
228 PM CDT
Second day of heat continues today across northern Illinois and
northwest Indiana where temperatures have warmed into the low
90s with dew points in the low to mid 70s. This afternoon, an axis
of convergence has developed from near Rutland, IL to near O`Hare
and the north Chicago metro, possibly the result of differential
heating from persistent thicker cirrus just northwest of that
line. This convergent axis represents the most likely area to see
an isolated shower or storm to develop this afternoon. A second
area of convergence is noted from near Kankakee to Gary, IN.
Recent AMDAR soundings out of Chicago indicate very weak if any
CIN and RAP analysis shows in excess of 2000 J/kg MLCAPE over the
forecast area. Despite the instability, lack of any synoptic scale
ascent (soundings how more subsident conditions in place) should
limit precip chances to stay fairly isolated along these areas of
low level convergence. Will have to keep an eye on any outflow
boundaries that may develop this afternoon as well. These slight
precip chances will wane with sunset this evening. Overnight lows
are only expected to be in the mid 70s with Chicago holding on to
80s in spots due to the urban heat island.
Heat continues again on Monday and expect another day with
temperatures into the low possibly mid 90s with dew points in the
low to mid 70s. Heat indices are forecast to be in the 100 to 105
range again on Monday. Given this will be the third day of 100+
heat indices, have opted to continue the heat advisory despite the
potential for falling just shy of the 105 criteria. The
cumulative effects of the heat will continue to take a toll.
Meanwhile, a cold front is progged to sag south across Wisconsin
through the day tomorrow likely reaching the state line by late
afternoon or early evening. Some models show outflow surging down
the lake which may result in earlier relief from the heat for some
locations near the lake if this occurs. Chances for showers and
thunderstorms will increase through the afternoon as the front
approaches. Dew points pooling into the mid 70s along and ahead of
the front will contribute to moderately strong instability,
though upper level flow continues to appear weak which may help to
mitigate the threat for organized severe weather. Very heavy
rainfall and pulse-severe appear to be a distinct possibility
327 PM CDT
Monday night through Sunday...
Overview...Looking at a wet start to the week as a cold front/low
pressure trough stalls over the forecast area Tuesday and Wednesday.
Temperatures will vary widely Tuesday from lakefront temps around 70
to upper 80s and heat indices in the upper 90s south of I-80. We
get a little relief from the heat mid week, but widespread precip is
expected to return late in the week with a low pressure system.
The front stalls over the southern portion of the forecast area
Monday night. Temps north of the boundary will be in the mid 70s to
low 80s away from the lake. Lakefront temps will be around 70 thanks
to flow off of the lake, while areas south of I-80 will be in the
upper 80s. Additional showers and storms are expected, and heavy
downpours are likely with precipitable water values over 2 inches. 2
inches is an abnormally amount of precipitable water for this time of
year. CAPE values are forecast to be around 1500 J/kg, but shear
will be less than 20 kt. Therefore, a few storms may pulse up, but
widespread severe storms are not expected at this time. Steering
flow around 20 MPH will lead to slowly moving storms, so flash
flooding may be possible if storms train.
The boundary shifts south Wednesday as does the chance of showers
and storms. Onshore flow continues leading to highs around 70 along
the lake, but mid 70s to low 80s elsewhere. An upper level
disturbance may trigger more showers and storms Thursday, but I have
low confidence in timing and location. Temps will be similar to
Widespread precip is more likely Friday as low pressure moves over
Iowa. The low moves over the lake Saturday, and there may be more
showers and storms Saturday. Temps continue to be near normal, but
cooler near the lake.
A record warm low is probable for Chicago for June 17. Here are
the standing records for Chicago and Rockford:
Sun Jun 17 Low 77 (1984)
Mon Jun 18 High 98 (1954) 99 (1994)
Low 77 (1921) 74 (1905)
For the 00Z TAFs...
Main forecast concerns center around the threat of thunderstorms
with heavy rain, particularly very late Monday afternoon and into
the evening as a cold front begins to drop over the area.
The spotty showers and thunderstorms are quickly dissipating
across the area early this evening. Overall, tonight into early
Monday afternoon look quiet weather-wise. The only exception to
this will be if some thunderstorm activity well to our northwest
tonight tries to drive an outflow boundary and some isolated to
scattered storms southward over the area by daybreak Monday.
Currently confidence is this occurring is on the low side, so
there is currently no mention of such in the TAFs, but this
possibility will need to be monitored.
Otherwise, expect another hot day with west-southwest winds
gusting up close to 20 KT at times into the afternoon. Some
isolated afternoon storms could again develop over the area
Monday, as they did this afternoon, but the primary window for
thunderstorms looks to be very late Monday afternoon into the
evening (roughly 23z through 04z). This better chance of storms
will be associated with a cold front, which is expected to shift
over the terminals by early evening. In addition to the storms,
expect a wind shift out of the north-northeast following the
frontal passage. While the exact timing of storms into Monday
evening is still a bit uncertain, it does appear that there could
be a few hour period of storms. These storms are also likely to be
prolific rainfall producers. So a periods of heavy rainfall with
low visibilities possibly briefly under a mile will all be
possible with these storms.
327 PM CDT
Southwest winds continue until a front shifts down the lake
Monday. Models differ on how quickly the front will progress, and
I went with a slower solution. The front should clear the
southern end of the lake Monday evening, and winds will be north
to northeast 10-20 kt tonight. The front will stall over central
IL and IN, while a high pressure ridge will stretch from the
northern Great Plains through the northern Great Lakes into
southeast Ontario. Light northeast winds are expected through much
of this week. The next low will form over the Plains Thursday and
is forecast to reach the lake Saturday.
IL...Excessive Heat Warning...ILZ014 until 7 PM Monday.
ILZ033-ILZ039 until 7 PM Monday.
IN...Heat Advisory...INZ001-INZ002-INZ010-INZ011-INZ019 until 7 PM
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Area Forecast Discussion
National Weather Service Pueblo CO
241 PM MDT Sun Jun 17 2018
.SHORT TERM...(This evening through Monday)
Issued at 228 PM MDT Sun Jun 17 2018
South to southwest flow aloft will remain over the area tonight,
ahead of an upper level low centered over northern NV. A
disturbance will be slowly moving from northern NM, northeastward
across southeast CO tonight. For this evening, the models have been
consistent in showing the majority of precip from about the I-25
corridor counties and westward, with maybe some isold activity over
eastern areas. The HRRR and NAM have been consistent in showing the
highest precip chances this evening over the central mtns, the Pikes
Peak region and maybe southward into Pueblo and Huerfano counties.
QPF amounts in the GFS are higher than the NAM, and show from a
couple tenths of an inch over Teller and northern El Paso county to
around a half inch or a little more. Localized heavy rain will be a
concern, especially over burn scars, and possibly urban areas. It
looks like most of the precip will be over by about midnight, but
there could be a few lingering showers over northern area into the
late night. A strengthening surface low over the I-25 corridor of
southern CO into this evening will cause strong southerly winds over
the far southeast plains.
Drier weather is expected for Mon, although there could be some
isolated showers/tstms in areas mainly north of Highway 50. High
temps on Mon are expected to be around to a few degrees above
average, with upper 80s to mid 90s acrs the southeast plains, and
upper 70s to lower 80s in the Upper Arkansas River Valley and the
San Luis Valley.
.LONG TERM...(Monday night through Sunday)
Issued at 228 PM MDT Sun Jun 17 2018
Monday evening through early Tuesday...A lee surface trough will
shift east across the southeast Colorado plains, pushing a front
down the plains. Increased moisture behind the front and weak
upslope flow could lead to the development of an isolated shower
or thunderstorm along the Palmer Divide. Otherwise, the forecast
area will remain dry through Tuesday morning.
Tuesday through Wednesday...The long term forecast period begins
with a closed upper low filling in as it lifts northeast out of
the Great Basin and into the northern Rockies. Meanwhile, an
upper ridge begins to build over the southwest US. The addition of
high pressure over the southeast US will cause south/southeast
low level flow from the Texas Gulf Coast into southern Colorado,
increasing TPW to around an inch again. As the upper low lifts
northeast, a series of shortwave troughs will advance through
Colorado. These features will keep a surface boundary draped
across the plains each day. The combination of large scale forcing
for ascent, surface frontogenesis, and above average moisture
will allow for the development of showers and thunderstorms across
the eastern mountains and plains each afternoon/evening. Precip
chances appear to be greatest over the central and eastern
mountains and the plains east of the I-25 corridor, with more
isolated coverage across the I-25 corridor. The southwest
mountains will stay mainly dry. Given high TPW, heavy rain will be
possible with thunderstorms. While a strong thunderstorm with
small hail and gusty winds is possible, CAPE and shear will likely
be weak enough to limit the development of severe storms. Tuesday
will have high temperatures around 90 across the plains and 80 in
the high valleys, while temperatures on Wednesday will be cooler,
with highs in the low to mid 80s across the plains.
Thursday through Friday...As the upper ridge continues to build
over the southwest US Thursday into Friday, height rises and
associated QG descent will limit precip coverage. However, still
above average atmospheric moisture and weak embedded energy should
allow for isolated diurnal shower/thunderstorm chances across
most of the forecast area. Precip chances appear less on Friday
versus Thursday as moisture gets pushed out of the region. High
temperatures should be similar on Thursday as on Wednesday, but
will rise back into the upper 80s to near 90 on Friday.
Saturday through Sunday...Model solutions diverge significantly
during this period. The ECMWF advances a progressive shortwave
over Colorado by Saturday morning, while the GFS doesn`t bring it
in until Saturday night, and the Canadian even later. By this
period, GEFS has moderate spread in 500 mb heights. So, while it
is appearing probable a quick-moving shortwave brings increased
precip chances to the forecast area sometime this weekend, it is
still too early to determine more precisely when/where/what. -Line-
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 228 PM MDT Sun Jun 17 2018
Showers and thunderstorms will be possible at KCOS, KPUB and KALS
thru this evening. High resolution forecast models suggest a fairly
good chance for precip at KCOS and maybe KPUB later this evening,
which could continue until around 08Z. Drier weather is expected on
Mon, with breezy southerly winds in the afternoon.