Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/02/21

Area Forecast Discussion
National Weather Service Denver/Boulder CO
855 PM MDT Thu Jul 1 2021 .UPDATE... Issued at 855 PM MDT Thu Jul 1 2021 After a very active day from a hydro point of view (we issued 8 flash flood warnings and 21 urban and small stream flood advisories), the atmosphere has stabilized significantly. Latest radar and GOES-16 satellite imagery have a broken line of convection from western Logan to eastern Morgan to northwest Elbert County. There is no development upstream of our area either. The convection in eastern Colorado is producing some lightning and brief heavy rain, though we do not expect any more hydro highlights. It has been slowly weakening but expect the convection to keep going eastward until about midnight before weakening/diminishing and/or moving out of our CWA. With how stable the atmosphere is behind this line, we ended the flash flood watch ahead of schedule. Overall, the HRRR and HREF did a nice job with the convective evolution going on right now, and both weaken the convection by midnight and there doesn`t appear to be any redevelopment along or west of I-25. Updates to the forecast were generally minor, lowering min temps just a tad given latest trends and updating PoPs to reflect current trends, namely highest east of Fort Morgan to Agate, very low west of there, and tapering off after midnight across far eastern Colorado. Patchy fog may develop in Weld County where 2-4 inches of rain fell in the Greeley area. We`ll keep an eye out to see if it becomes widespread enough for a highlight. && .SHORT TERM...(This evening through Friday) Issued at 245 PM MDT Thu Jul 1 2021 Heavy rain and flash flooding will continue to be a concern across the area this evening, with a focus along the I-25 corridor from the Wyoming border towards Castle Rock. The recent slow moving/backbuilding storm over Greeley was able to produce upwards of 3-4.5 inches of rain within about 2 hours, which has produced flash flooding across the city. Not much was changed to the grid forecast for the rest of the afternoon. Outflow from previous storms to the east of the metro has worked all the way into the lower portions of the Foothills, with convective activity gradually shifting eastward along with it. An 18z sounding from Colorado State University near FNL had MLCAPEs near 1750 J/kg... along with PWATs near 1.20 inches... and very weak low/mid-level flow. While instability will diminish with time, heavy rainfall will be likely until convection diminishes just before midnight. Tonight will see just a few scattered showers around after midnight with continued moisture sitting around the area. There could be some patchy fog in a few spots, especially where the better rains fall this evening. Conditions are largely similar tomorrow, but rainfall should be more focused on the higher terrain. It looks like tomorrow will be a bit warmer and drier, with a little less instability. The main difference will be less of an upslope component to the low-level wind, with slightly improved flow aloft. The end result should be scattered storms with heavy rain, but with less coverage and less intense rainfall rates. Most of our concerns will be focused on the burn areas. .LONG TERM...(Friday night through Thursday) Issued at 245 PM MDT Thu Jul 1 2021 The upper level ridge pushed northwest out of the desert southwest and into the four corners region through Friday evening with subsidence persisting through the holiday weekend. This will help to bring daytime temperatures closer to seasonal normals and slightly above with highs in the upper 80s to lower 90s by Sunday. Models show moisture moving in under the ridge with PWat values increasing to close to an inch across the eastern portions of the state. Lapse rates will improve by the afternoon hours with ML CAPEs from 600 to 850 that will provide the ingredients for some afternoon convection both Saturday and Sunday. Flow aloft will be slightly faster than previous days which will aid in keeping the storms moving but there is still some concern for flooding under the stronger storms through the weekend. By Monday the upper ridge extends across most of the southwest region with continued monsoon influence providing for elevated PWat values. High temperatures will be above seasonal normals on Monday. Models show a weak shortwave embedded in the flow aloft Monday night into Tuesday with increased coverage of storms for Monday late afternoon and evening. This will push out on Tuesday leaving slightly cooler temperatures with highs dropping back into the 80s on Tuesday. There is some slight model differences within the EC and GFS suites that has surface flow a tad more east to northeast on the EC creating some enhanced lift and more widespread storm coverage Tuesday afternoon and into the evening. Wednesday will see increased influence from the upper ridge with dry conditions expected and temperatures reaching back into the 90s. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 855 PM MDT Thu Jul 1 2021 Convection is well east of the terminals and we do not expect any redevelopment tonight. Winds in general will remain light throughout tonight, out of the south at APA and DEN and 10 kts or less. Light and west at BJC. We are looking at the potential for radiation fog to develop in Weld County where heavy rain occurred today. The fog may make a run at DEN. It`s not a typical fog set up for DEN, thus for now we are handling with a VCFG. The fog, if it develops, and if it makes a run at the airport, should only last a few hours, roughly 5-8AM or so. By midday Friday winds should be southeast at the terminals and we expect TSRA to develop near the terminals after 3 or 4 PM, and possibly impact them like they did today, though the rain rates are not expected to result in reduced VIS like they did today. We expect variable wind gusts 20-30 kts associated with convection but it`s too early to include in the TAF right now.Still && .HYDROLOGY... Issued at 855 PM MDT Thu Jul 1 2021 Elevated flash flooding danger is also expected tomorrow across the burn areas. Moisture remains with storm motions still fairly slow, and heavy rainfall will be possible during the afternoon hours. Flash flood threat will turn limited for the weekend with some storms possible over the higher terrain for both Saturday and Sunday afternoons. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Schlatter SHORT TERM...Hiris LONG TERM...Bowen AVIATION...Schlatter HYDROLOGY...Hiris
Area Forecast Discussion
National Weather Service Boston/Norton MA
958 PM EDT Thu Jul 1 2021 .SYNOPSIS... Areas of showers and scattered thunderstorms will produce locally heavy rain tonight. Unsettled but much cooler Friday into the Fourth of July weekend. Scattered pop-up showers each day in the holiday weekend but not a washout in any one area. Brief dry weather Monday with a warm front arriving Monday night. Heat and humidity returns on Tuesday, ahead of a cold front that offers a greater chance for thunderstorms either later Tuesday or Wednesday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 10 PM update... Widespread showers with locally heavy rain moving across SNE this evening in response to large scale forcing within the right entrance region of the upper jet and deep moist thermodynamic profile. PWATs 1.7 to 2 inches with deep warm cloud depths providing a favorable environment for warm rain processes and efficient rainfall rates. There are potentially two areas of concern for heav rainfall and localized flooding. One area near the Mass Pike where there are somewhat heavier rainfall rates. Weak front across northern MA providing some low level convergence and there is enough instability with MUCAPES around 500 J/kg to enhance rainfall rates. HRRR and 3km NAM target this area for very heavy rainfall through 06z. Amounts of 2-4 inches may be overdone given current rainfall rates but could see locally up to 2 inches with some urban and poor drainage street flooding. Rainfall rates likely to diminish after 06z in the interior. Second area is across SE New Eng, particularly over the Cape/Islands as convective cluster along the nose of a developing low level jet lifts NE along the coast through the overnight period with a few t-storms enhancing rainfall rates. The low level jet moves east of New Eng late tonight. Winds will shift to the northeast and increase late tonight as the cold front gradually moves through. This will result in cooler temperatures. Anticipating overnight low temperatures in the 60s across the region, but there may be a few upper 50 degree readings along northern portions of the region. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Highlights * Fairly widespread showers across the region Friday morning becoming more scattered in nature during the afternoon. Scattered showers persist Friday night. Trough digs into the eastern Great Lakes and Mid Atlantic on Friday and Friday night. Should see a frontal boundary to the south as the cold front moves offshore. Will have a surface trough extend over southern New England on Friday from the departing broad low. Another low rides along the frontal boundary to the south Friday night. Friday... Will still have a 1.5-2 inch PWAT plume over a decent portion of southern New England Friday morning, but with the low lifting out this plume will push offshore during the afternoon. This keeps us in the 1-1.5 inch range for the afternoon. Still have decent warm cloud layer depths between 3-4 km. Thinking there still could potentially be some heavy rain in a few showers especially earlier in the day given the proximity to the broad low. Cannot be ruled out during the afternoon, but forcing becomes a bit more limited and activity should be more scattered in nature. Given the track of the low am anticipating a non-diurnal temperature trend. Should see the warmest readings across the region during the morning with temperatures dropping during the day. This is all due to the northeasterly flow due to the low moving through. Aloft will have cold air advecting in 7-10 degree Celsius 925 hPa air! Temperatures will stay generally in the 60s, but will drop into the 50s for some spots during the afternoon. Friday night... Expecting another wave of low pressure to ride along the frontal boundary that is offshore. Given the persistent onshore flow, upper level forcing and 1-1.5 inch PWATS could have some scattered shower activity. Will still have persistent NE flow keeping 925 hPa temperatures in the 8-10 degree Celsius range. The result will be low temperatures bottoming out in the 50s across southern New England. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights: * Unsettled and generally cloudy Fourth of July weekend, periods of pop-up showers but not a washout. Well below normal temps Saturday (upper 50s-low 60s!), and just less below-normal for the Fourth of July holiday. * Warm front late Mon/Mon nite brings scattered showers, possible garden variety t-storms. Turning more humid Mon nite. * Hot and humid Tuesday with mid/upper 90s heat indices; somewhat cooler and a little less humid Wed. Possible thunder either Tues or Wed depending on a cold front. Details: Fourth of July Weekend: The story for the Fourth of July Weekend is the generally unsettled weather conditions and cooler than normal temperatures for Saturday and the Sunday Fourth of July holiday. In terms of temperatures, the most anomalous of the two days is Saturday and for most highs may struggle to reach the mid 60s with upper 50s to lower-mid 60s common. Possible we could approach record low high-temperatures on Saturday July 3rd, with temperatures more reminiscent of mid-May than early-July. Looking at Fourth of July holiday climatology for our four climate sites (Boston, Providence, Worcester and Hartford/Windsor Locks)...with forecast Fourth of July high temperatures in the upper 60s to mid 70s, it appears we are in store for one of the coolest Fourth of July holidays since 2015; the exception being Boston which recorded a high temperature of 70 on the Fourth just last year in 2020. So for Saturday: upper low and associated cooler pocket of air aloft initially near the lower Hudson Valley to migrate slowly NE across Southern New England. Periods of light pop-up showers with better coverage during the late-morning to mid/late afternoon will dot the landscape and while generally unsettled, not expecting a washout with limited QPF. That said, plenty of low-level moisture trapped underneath a shallow inversion and when combined with northeast onshore winds, it sets the stage for a cool July 3rd with lots of low clouds around. Have lowered temperatures significantly compared to the warmer NBM guidance, essentially a blend of the raw GFS and NAM. Again looking for highs upper 50s to mid 60s for most - definitely a long sleeve and light jacket sort of day! Periodic, intermittent showers into Sat night, though still a rather cool night with lows mid 50s to low 60s. For Sunday/Fourth of July: Upper low will continue to pull away with a renewed risk (Chance) for pop-up light showers during the morning to early-afternoon. Initial overcast, but better odds for some breaks in clouds during the second half of the day and night as winds turn more light northerly/northwesterly. Won`t be fully clear both day and night, but enough breaks for highs upper 60s to mid 70s; lows upper 50s to lower 60s. It may not be an ideal beach day, but the prolonged onshore flow and related leftover swell from the weekend, it`s possible there may be a need for either a rip current statement or (less probable) a high surf advisory on Sunday and/or Monday for east-facing coasts. Monday: Mid/upper flow turns more zonal by Mon, with modest height rises for Mon afternoon. A warm front comes in for later Monday into Monday night, associated with summerlike 850 mb air (mid-teens Celsius) in the warm sector. This should bring a risk for showers, possibly a rumble of thunder given some elevated instability. Highs low to mid 80s, but Monday night looks to turn muggy/humid with lows mid/upper 60s with similar dewpoints. As mentioned, we may need to consider either a rip current statement or (less likely) a high-surf advisory for the east-facing coasts. Tuesday and Wednesday: Hot and humid Tuesday (dewpoints back to the muggy mid 60s to lower 70s), though not to the extent of the stretch of hot and humid weather experienced recently. That said, heat indices may approach the mid to upper 90s on Tuesday depending on how much warming we do get; it looks like we`ll fall short of one-day Heat Advisory criteria and lower Heat Indices on Wed also make the consecutive 95+ heat index criteria less likely to be achieved as well. Nonetheless still quite hot for Tuesday. This occurs ahead of a cold front, the timing of which varies across most of the NWP. Potential exists for heavy SHRA/TSRA depending on the timing. Kept a rather generic/broad brushed Chance PoP both days until better agreement exists on the timing of the frontal passage. Highs Tues into the upper 80s lower 90s, with lows around 70 except mid-upper 60s for the Berks. Somewhat cooler mid to upper 80s on Wed, lows in the 60s. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z TAF Update: Tonight: High confidence in trends/categories, moderate on timing. VFR/MVFR initially. General idea is for deterioration to IFR- LIFR as sfc low moves ENE through CT-RI and SE MA through overnight, though the timing is still no better than moderate confidence. Initial rains now across western MA/northern CT will spread eastward thru 03z for areas north of I-95, with VFR- MVFR visby rains continuing thru overnight. Period of heavy SHRA/embedded TSRA at PVD and South Coast/Cape and Islands between 01-04z, with brief IFR to local/brief LIFR visby possible. Left as just a 3 SM SHRA but will tempo lower category visbys. Winds will back to E to NE/N mainly N/W of I-95, but remain SW across Cape and Islands until a shift to NW/N around pre-dawn. Friday...Moderate confidence. Widespread MVFR/IFR conditions. Showers likely at times during the morning, but more scattered in nature during the afternoon. NE winds at 5-10 kts. Gusts of 15-25 kt over E and NE MA with the highest gusts over NE MA. Friday night...Moderate confidence. Widespread MVFR/IFR conditions across southern New England. Scattered rain showers continue with winds out of the NE to NNE at 5-10 kts. Could see some 15-20 kt gusts along the coastal plain. KBOS TAF...High confidence in trends. Moderate confidence on timing of lower ceilings moving in. KBDL TAF...High confidence in trends. Moderate confidence on timing of lower ceilings moving in. Outlook /Saturday through Tuesday/... Saturday: Mainly VFR, with areas IFR possible. Breezy. Chance SHRA. Saturday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA. Independence Day: Mainly VFR, with areas MVFR possible. Slight chance SHRA. Sunday Night: VFR. Slight chance SHRA. Monday through Monday Night: VFR. Tuesday: VFR. Breezy. Slight chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Have hoisted a Small Craft Advisory for the Outer Waters, Cape Cod Bay, Ipswich and MA Bay from Friday AM through Friday night. Tonight...High confidence Winds out of the S/SW across the southern waters at speeds of 10-15 kts. Expect the eastern waters to start off with light winds, but shift to the E/NE late tonight and increase to 10-20 kts. Could have some gusts up to 20 kts toward daybreak. Seas 2-4 feet. May see some 5 ft seas across the outer southern waters toward daybreak. Numerous showers with perhaps a few embedded thunderstorms. Friday...High confidence Will see a period of NE winds at 15-25 kts across the eastern waters. Gusts of 25-30 kts and there could be a few brief gale force gusts. The southern waters will see winds shift to the northeast as a cold front pushes through. Wind speeds increasing to 10-15 kts late in the afternoon across the southern waters. Seas building to 6-9 ft across E/NE waters and 3-5 ft for the southern Waters. Have hoisted a SCA, but held off from high surf advisories given the cool temperatures and scattered rain showers. Seas 3-7 feet Friday night with NE winds at 10-20 kts. Outlook /Saturday through Tuesday/... Saturday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers. Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Independence Day through Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday through Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Winds less than 25 kt. Seas up to 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM Friday to 5 AM EDT Saturday for ANZ231. Small Craft Advisory from 8 AM Friday to 8 AM EDT Saturday for ANZ250-251-254>256. && $$ SYNOPSIS...BL/Loconto NEAR TERM...KJC SHORT TERM...BL LONG TERM...Loconto AVIATION...BL/Loconto MARINE...BL/Loconto
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1120 PM EDT Thu Jul 1 2021 .SYNOPSIS... A cool and wet period late this week with low pressure amplifying south of us tonight, bringing widespread rains to the forecast area into tomorrow morning. The system departs east tomorrow night and gives a brief dry break in the action, however a broad trough will persist across Northern New England through the weekend, bringing cool conditions and showers at times. The trough departs on Monday, and ridging returns early next week with warmer weather. Midweek next week the forecast become less certain, but above normal temperatures appear increasingly likely. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 1120 PM Update: Update to Marine only...see below. 9 PM Update: Have lowered temperatures where rainfall has been steadiest in line with evening observations. Otherwise... forecast largely in good shape with decent rainfall rates now reaching southern NH /0.1-0.2" per hour/. Low pressure near New York City is moving ENE in line with current pressure fall analysis with rainfall area expanding on it/s northern flank. 00Z GYX RAOB showed 1.45" PWATs with a deepening ENE flow in the boundary layer. Rain will continue to expand northward overnight with a few more hours of convective elements possible before the deepening cold dome under strengthening NE flow will erode remaining instability. 530 PM Update: Given increasing confidence in area of widespread precipitation tonight..boosted PoPs in line with recent time lagged HRRR and short term model consensus. Otherwise...going forecast in good shape. Previous discussion below... The final nail in the coffin of our recent heat wave is hammered down tonight as a backdoor cold front arriving from the northeast partners with amplifying low pressure /a summertime Nor`easter/ to the south... bringing widespread rains to the forecast area starting tonight and lasting into tomorrow. Temperatures will cool into the 50s to near 60 tonight. A surface trough draped broadly over the forecast area is already showing signs of organizing near the Mid-Atlantic coast with rain picking up in coverage and intensity over southern New England. As low pressure crosses Cape Cod tonight, rain will overspread most of the area from the southwest with totals ranging from AOB a quarter inch near the international border to about an inch for southern zones. Hires guidance continues to home in on a deformation zone draped roughly from Sullivan Co NH across to the Midcoast... which would lead to locally higher rainfall totals. Am not immediately concerned about flooding issues with this deft band since lapse rates are poor which will prevent convective rainfall rates... however if moderate rainfall sits over the same area for a couple/few hours it could lead to some ponding and poor drainage issues. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday wraps up the work week with some weather-whiplash when compared to how it started. A summertime Nor`easter passes through the Gulf of Maine tomorrow with rain, overcast, and temperatures limited to the 50s and 60s. Steady rain over the coastal plain near the low pressure center crosses during the morning with more scattered activity underneath cyclonic flow later in the day... the latter of which will taper off to isolated showers overnight. Northeast winds continue into tomorrow night with temperatures cooling into the mid-50s... to as cool as the mid-40s for northern valleys, especially if they can clear out. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Overview...The long term begins with widespread showers on Saturday and Sunday, although Saturday looks like the wetter of the two. A drying and warming trend begins on Monday with the next significant chance for precipitation coming toward mid-week when a cold front may cross through New England. Impacts...No significant impacts are anticipated at this time...but will continue to monitor temperatures and heat indices on Tuesday for possible heat-related headlines for southern areas. Forecast Details...The holiday weekend begins with an upper level trough just to our west and a broad baroclinic zone with weak areas of low pressure along it over the western Atlantic. In between, plenty of cloud cover and a good chance for showers are on tap for Saturday. Highs will remain similar to Friday, ranging throughout the 60s. By Sunday morning, the trough passes overhead and looks to be centered east of the CWA...but wraparound showers will be possible on the backside of the trough on Sunday. Temperatures will be warmer though, rising into the mid 60s to lower 70s. An upper level ridge begins to build into the northeast U.S. on Monday, bringing drier conditions and warmer temperatures; highs on Monday will be closer to normal, ranging from the upper 70s to lower 80s. By Tuesday morning, the global models are in better agreement in their latest runs that a cold front will drop south of out of Canada on Tuesday, possibly bringing showers and thunderstorms to the region Tuesday afternoon and evening ahead of it. Tuesday looks like the warmest day of the period ahead of the front with highs ranging from the mid 80s to near 90. Current apparent temperature grids show some southern areas with an hour or two of heat indices at 95 will continue to monitor the potential for heat- related headlines Tuesday afternoon. The front does not arrive until Wednesday morning, allowing precipitation chances to continue into Tuesday night and Wednesday. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Short Term... Summary: Low pressure tracking southeast of the region will bring deteriorating conditions tonight in rain before rain tapers to showers during the day Friday with some improvement to conditions by afternoon and evening before some fog/stratus redevelop Friday night. Restrictions: CIGS deteriorate to IFR for all but HIE overnight (MVFR there) with some LIFR possible for coastal terminals with rain at all sites. Rain tapers to showers with improvement to MVFR for the day on Friday. Confidence decreases Friday night with continued gradual improvement likely...but some potential for MVFR stratus to continue through the night. Winds: North/northeasterly winds strengthen to 10kts overnight before strengthening to 10g18kts for the day on Friday. Winds from the north and northeast continue Friday night around 5kts. Lightning: Very low potential for lightning through midnight for LEB- PWM-CON-MHT-PSM...with no thunderstorms beyond this through Friday night. LLWS: There is some potential for 2kft winds to increase to 30+ kts from the northeast in the 06-14Z timeframe...but confidence in this occurrence remains too low to include in the current TAFs. No LLWS expected Friday afternoon and night. Long Term...Widespread MVFR conditions on Saturday in showers and low ceilings. Some improvement likely on Sunday, especially for inland terminals, but showers with brief MVFR restrictions remain possible. Widespread VFR conditions look likely by Sunday night and continue through the remainder of the period. && .MARINE... Short Term... 1120 PM Update: With recent HRRR runs as well as new 3km NAM continuing to support gales over the outer waters with support from other high res models...will upgrade the outer waters to gale warnings at this time and add Penobscot Bay to the SCA. Do not foresee the need for additional adjustments. 9pm update: Mesoscale guidance continues to slowly increase northeasterly wind expectations overnight with gales increasingly likely over the outer waters towards daybreak. Have boosted winds some and added Casco Bay to the SCA given the trend...but will continue to watch the evolution of the surface low before making any upgrades. Did mention gale potential in the updated Hazardous Weather Outlook. Previous discussion below... Low pressure amplifies and approaches from the southwest tonight with increasing northeast winds. Winds over the outer waters will increase to 10-20 kts sustained with frequent wind gusts to 30 kts. There is a small chance that Gale Force gusts will be realized several miles from shore, but without the confidence to upgrade to gales... if this were to occur, this would be during the late Friday morning time frame and be accompanied by rain. Seas will come up to 4-6 ft near shore during this time, and will approach 10 ft for a brief time well out over the waters. Winds will back down but remain out of the northeast tomorrow night although seas will remain elevated into Saturday. Long Term...Showers will be possible Saturday and Sunday with low pressure passing near or over the Gulf of Maine. Northerly winds are expected through the weekend before becoming southerly early next week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ151-153. Gale Warning until 6 PM EDT Friday for ANZ150-152-154. && $$ NEAR TERM UPDATE...Arnott AVIATION...Arnott MARINE UPDATE...Arnott
Area Forecast Discussion
National Weather Service Phoenix AZ
432 PM MST Thu Jul 1 2021 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Scattered showers and thunderstorms will be common over the higher terrain and more isolated on the lower elevations the rest of the week. Gusty winds with localized blowing dust, and localized heavy rain/flooding will be the main impacts. A slow decline in storm activity begins by early next week, but daily storm chances over the eastern Arizona high terrain should persist. Temperatures will be near normal the rest of this week before increasing slightly early next week. && .DISCUSSION... Convection today developed earlier than it did yesterday, by 9:30 AM across the northern AZ high terrain, White Mtns, and in southeast AZ. However, for the most part, storms have been less intense. More so, the coverage of strong/marginally severe storms have been less. One factor may be slightly lower CAPE values seen on 12Z morning soundings and RAP mesoanalysis. Steering flow is still very week with 850-300 mb mean winds analyzed around 5-10 kts, so storms have been nearly stationary. PWAT values have fallen slightly, but mixing ratios remain near 10-11 g/kg, so storms have still been efficient rain producers with rain rates upwards of 0.5-1.0"/hr. Flooding impacts over very localized terrain areas will be possible with any storms that experience an extended resonance times over one area before dissipating. DCAPE is also notably lower today across southeast AZ, so the chance for strong downburst/outflow winds is lower today in Gila and Pinal county. HREF probability of >35 mph winds is around 20-30% chance. Wind impacts and blowing dust potential will be slightly higher out in the Kofas area of Yuma and La Paz counties, where DCAPE values are higher. While convection should dissipate after sunset, a weak inverted trough moving northwest out of Sonora Friday morning may generate isolated to scattered ACCAS showers. Most CAMs favor progression of the wave, and best shower chances, through portions of southwest AZ and southeast CA, but coverage could extend up into south-central AZ. Forecast soundings in the Yuma area Friday morning support embedded thunder chances as well, with minimal elevated CAPE. Any stronger shower could produce gusty downburst winds. .PREVIOUS DISCUSSION... For Friday, there are signs of a decent moisture push out of northern Mexico early in the morning with some potential shower activity moving into southwest and portions of south-central AZ. This may be partially due to the inverted trough slowly moving westward along the border, but also possibly a reflection of the increasing broad southeasterly flow ramping up across the region as the upper level high center shifts into the Four Corners area. Low level mixing ratios do not really increase all that much on Friday, but the higher values do spread westward to the Lower CO River Valley. The HREF does show a slight increase in storm activity for Friday across southeast AZ and the high terrain east of Phoenix as well as overall MUCAPEs through south- central Arizona. The slight uptick in moisture and instability on Friday should result in a bit better chances of storms across the south- central AZ deserts, but weak winds aloft and a very weak southeasterly steering flow would likely again limit storm longevity. Storm chances will remain over the upcoming weekend with both days showing fairly plentiful moisture, possibly even too much moisture aloft resulting in possible issues with extensive cloudiness and the lack of instability. GEFS shows PWATs increasing to around 1.75" by Saturday morning, likely due to a deepening southeasterly fetch of moisture out of northern Mexico. Models show the upper level ridge is likely to remain parked over northern AZ over the weekend with very weak flow aloft across southern Arizona. This scenario could mean we will be quite active on one or both (unlikely) of the days, but it may also just result in modestly unstable, but fairly capped environment. Afternoon/evening storm chances will likely depend on the amount of leftover clouds from the previous night/morning and if there is any help from possible disturbances/inverted troughs. If there ends up being plentiful moisture, storm threats are likely to transition more toward heavy rainfall and localized flooding (as long as instability is present). After near normal temperatures through Friday, temperature guidance for Saturday and Sunday shows a much higher spread. Highs are still most likely to reach near normals over the weekend, but due to the higher potential for clouds and storms there is definitely more room for highs barely making it to 100 degrees in some areas. A subtle southward shift in the position of the upper level high center looks likely for early next week and this should result in diminishing moisture and lower storm chances by Monday or Tuesday. As of now, the first half of next week will favor storm chances over the eastern Arizona high terrain with limited chances over the lower deserts. Temperatures for the first half of next week are also likely to creep upward slightly with fairly high (40-60%) probabilities of the western deserts reaching 110 degrees again, while Phoenix`s probability of reaching 110 degrees mostly stays below 30%. && .AVIATION...Updated at 2330Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Westerly to northwesterly winds will predominate across most of the TAF sites through this afternoon with speeds reaching 8-12 kts and occasionally gusting to 18-22 kts. There is less thunderstorm activity today compared to previous days, with diminishing chances for any storms within the terminal area (10-15%) through this evening. However, the few distant thunderstorms that are out there still have the potential for sending outflow winds that could cause abrupt wind changes. Right now, one boundary is being tracked east of KIWA but latest radar trends indicate this boundary weakening and unlikely to reach any of the terminals. Otherwise, a few periods of southerly to variable winds are possible tonight a few hours after sunset as the overnight easterly winds become predominate. For tomorrow, there is a low chance for isolated thunderstorms south of the Phoenix area early Friday morning, but current forecast does not have this impacting the Phoenix area. Winds will shift westerly again by the early afternoon as guidance trends indicate an uptick in thunderstorm development in the vicinity between 00/04z with the threat for multiple outflow boundaries and wind shifts. Southeast California/Southwest Arizona including KIPL and KBLH: There are no major aviation weather concerns as convection should remain east of KBLH and south of the US/MX border. Any outflow winds from these storms will likely reinforce the predominate winds. At KIPL, south-southeasterly winds will predominate through the forecast while southerly winds will remain at KBLH. && .FIRE WEATHER... Sunday through Thursday: High pressure is expected to become centered over Arizona over the weekend. A slow decline in atmospheric moisture is also anticipated to begin by early next week. Thus, the best potential for storms with locally heavy rain looks to be this weekend. Otherwise, a familiar Monsoon season pattern will be in place with storms primarily focused over the higher terrain producing outflows that spread to the lower deserts and in turn generate isolated new storms. Temperatures will start off near normals followed by slight warming early next week. Min RH values will generally be in the 20-30% range through Sunday before decreasing to 15-25% on Tuesday. Max RHs will be 40-60% for most areas through Monday morning before decreasing to 30-50% starting Tuesday. As the moisture decreases, temperatures will rise slightly, with highs around 110 degrees by early next week. Apart from thunderstorms, wind patterns will follow familiar diurnal patterns. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Benedict PREVIOUS DISCUSSION...Kuhlman AVIATION...AD FIRE WEATHER...Benedict/Kuhlman