Updated Thu 08/31 @ 5:25 PM — The strong upper level ridge (H) centered over New Mexico and Texas this afternoon will continue to expand northward and eastward through at least Monday—
Current Water Vapor Satellite Image with superimposed RAP model windstreams and 500-1000mb thickness (orange contours/orange arrows) will expand eastward and northward, giving us increasingly warm to hot weather by Sunday. (Click on image for a larger view.)
By Labor Day, the NAEFS continues to forecast extraordinarily high temperatures for the beginning of September—
NAEFS forecast high temperature for Monday, Labor Day. (Click on image for a larger view.)
Luckily, dew points won’t be too bad, probably only in the mid 60s at the hottest point in the day.
There will likely be no rain until next Thursday!
Thursday and Weekend Outlook
Updated Wed 08/30 @ 7:55 PM —Beautiful, dry and increasingly warm [hot] weather is in store for us over the next several days.
The high cirrus cloud shield noticeable today will be with us again Thursday morning, which is the outflow moisture from the remnants of Hurricane Idalia. This will move eastward and blue skies are expected Thursday afternoon.
Sunny with increasingly warmer temperatures Friday and Saturday.
A strong upper level ridge of high pressure (another ‘heat dome’) will be developing in the middle of the country and moving eastward. By Sunday, we’ll have above average temperatures approaching 90º.
By Monday, things get seriously hot—
Todays’s 12z NAEFS shows high temperatures by Monday to be more like July than September. (Click on image for a larger view.)
By Tuesday, rather extreme high temperatures for September are possible here—
NAEFS high temperature forecast for next Tuesday! (Click on image for a larger view.)
There’s not likely to be much if any rain over the next 7 days.
Updated Tue 08/29 @ 9:06 PM — A cold front will move through between 4 AM and 7 AM Wednesday morning with showers. The GFS has dialed back the rainfall considerably with this frontal passage. Skies will clear for sunshine about 10 AM.
18zHRDPS 1 hour rainfall at 6 AM Wednesday. (Click on image for a larger view.)
As for Hurricane Idalia, it seems to be speeding up yet still intensifying. Here’s the latest Hurricane HWRF model forecast at 8 AM—
18z HWRF model forecast at 8 AM Wednesday with accumulated rainfall. (Click on image for a larger view.)
Tuesday Forecast Update
Updated Tue 08/29 @ 8:34 AM — I’m updating my Tuesday forecast to be cloudy AND with a chance of a few showers in the afternoon, mostly between 2 and 6 PM. Most areas will not see showers this afternoon.
06z HRDPS forecast showing the total rainfall from showers by 6PM today. Most areas just cloudy. (Click on image for a larger view.)
The main line of showers with the cold front moves through about 4-5 AM Wednesday morning. Clearing with sunshine expected by mid to late morning on Wednesday.
Tuesday Forecast
Updated Mon 08/28 @ 8:21 PM — It looked like it might rain all day today, but the models kept us dry and such was the case.
Tuesday is looking even cloudier and more muggy than today. A few scattered showers before daybreak, but most of the day expected to be very cloudy with little to no rain. There will be a noticeable increase in humidity, some of it directly coming from the outflow of Hurricane Franklin.
An approaching cold front will bring a gradually increasing chance of showers late Tuesday afternoon. Increasing chances by 11 PM to midnight, with showers and thunderstorms expected after midnight into 4 or 5 AM. Clearing Wednesday morning.
All model forecasts keep tropical storm/Hurricane Idalia to our southeast with no direct effects. However tropical systems play havoc with model forecasts. The latest GFS suggests some lingering showers along the Jersey shore on Wednesday.
Today’s 18z GFS forecast for 12 noon Wednesday shows Hurricane Franklin and the tropical storm remnants of Hurricane Idalia. The mid level trough (blue line) will keep the storms from advancing to our area. The storm tracks will likely remain parallel to the 576 thickness line (wavy orange line) (Click on image for a larger view.)
Previously Posted Sun 7:58 PM —
A few days ago, it looked like our weather might be affected, at least indirectly, by two hurricanes. Both systems are now forecast to move far off to our east and south by Wednesday.
Latest GFS forecast (18z) showing both tropical systems at 1 PM Wednesday. (Click on image for a larger view.)
While we will escape most of the direct effects of this storms, an easterly flow will keep things cool and cloudy on Monday and the outflow moisture from Franklin in combination with an upper air trough will bring a chance of rain on Tuesday.
Updated Fri 08/25 @ 10:31 AM — The front moved though this morning.
This morning’s radar and RAP model overlay shows the showers have moved off. The lingering mid-level trough (dashed orange line) will move east and we’ll likely see a mix of sun and clouds for the rest of the day.
Last night’s forecast still holds:
Following the front, It will become quite humid with dew points in the low 70s by noontime. Some sunshine may break through late morning and early afternoon, but scattered showers are possible any time during the mid to late afternoon.
The only thing to add: Many of this morning’s models have little in the way of additional showers today. Additional showers, if any, will be widely scattered and most likely late afternoon or evening.
Friday’s Forecast
Updated Thu 08/24 @ 7:33 PM — A warm front will move through during Friday’s early morning hours (2 AM- 8 AM) with showers and thunderstorms. CAPE values are low, so no severe weather expected. However PWAT values are in the high (2.1″ to 2.2) range so some locally heavy downpours are possible, especially 5 AM to 7 AM.
Today’s 18z HREF accumulated rainfall forecast through noon on Friday. (Click on image for a larger view.)
Following the front, It will become quite humid with dew points in the low 70s by noontime. Some sunshine may break through late morning and early afternoon, but scattered showers are possible any time during the mid to late afternoon.
A cold front moves through Friday night with scattered showers. The cold front looks to be slow moving and not distinct. Only scattered showers or thundershowers expected at this time, but that may change.
Thu 4:22 PM Forecast Review — This morning’s forecast went as predicted, but the heavier band of showers moving through this afternoon wasn’t predicted by last night’s models.
Current Radar at 4 PM shows bands of rain not predicted. (Click on image for a larger view.)
Over the next few days, we’ll likely see that this won’t be the only forecast that goes astray.
As mentioned earlier this week “These sort of situations with stalled fronts and moisture moving over a ridge are difficult to forecast accurately. Small movements of the boundary will cause large differences in the amount of rain any area receives.”
We have the additional complications of a tropical system in the western Atlantic and a potential tropical disturbance developing off of the western Florida coast. For reasons I don’t understand (and my research has turned up empty), tropical systems in the picture seem to play havoc with model forecast accuracy.
Thursday Forecast
Updated Wed 08/23 @ 7:53 PM — A disturbance in the upper flow still appears to move mostly to our south and west tonight, along with the significant rainfall—
Water Vapor image with radar and RAP jet stream level wind streams (Click on image for a larger view.)
It will be mostly cloudy on Thursday with light showers mostly in the morning hours. Total rainfall through Thursday will be very light, especially from Philadelphia eastward, according to the HREF—
HREF total rainfall through Thursday at 8 PM. (The HRDPS has even lower amounts of rainfall from Philadelphia eastward.) (Click on image for a larger view.)
(Even lower rainfall amounts tonight and Thursday morning, according to the HRDPS.)
Rainfall from an approaching warm front Thursday night into Friday morning will likely be more substantial.
Wednesday Forecast Update
Updated Wed 08/23 @ 10:45 AM — The period from late Wednesday throughThursday is looking much less rainy than the HREF had forecast. Indeed, the HRRR and other models have moved towards the HRDPS which has been forecasting little in the way of rain here. (Showers move to our south and any showers moving towards us dissipate.) That’s why I began this week’s weather blog with “Unfavorable Pattern for Rain”
This morning’s 12z HRRR has joined the HRDPS in forecasting most of the significant rain will move to our south and north. (Some very light showers are still possible later tonight near the city. ) More significant showers possible Thursday night as a warm front moves northward. (Click on image for a larger view.)
Wednesday Forecast
Updated Tue 08/22 @ 8:36 PM — The cold front moved through early today and Tuesday was delightful. The frontal boundary has hit metaphorical wall and has advanced southward as far as the heat dome will allow. The boundary is pseudo stationary and impulses traveling over the top of the dome (as shown in yesterday’s graphic) will begin to affect our weather Wednesday.
Some of the moisture, possibly from Hillary, will advance over us with considerable cloud cover on Wednesday—
NAM forecast for Wednesday 3 PM shows clouds (dark) and rain advancing towards us over the heat dome. The wavy orange line (thickness line) is the approximate boundary of the hot/humid air. (Click on image for a larger view.)
These sort of situations with stalled fronts and moisture moving over a ridge are difficult to forecast accurately. Small movements of the boundary will cause large differences in the amount of rain any area receives.
Currently, our HREF model forecast is for rain moving in around late evening Wednesday and continuing through at least Thursday morning and possibly on and off through much of Thursday. Interestingly, the latest HRDPS has the rain totally missing our area and moving to our south.
I expect the Thursday through Friday forecast to have higher an average uncertainty, low confidence.
A Cold Front Pushes Heat Dome to our South
Updated Mon 08/21 @ 7:45 PM —We didn’t get as warm or as humid today as had been forecast, probably due to the layer of smoke in the atmosphere. (High in Philadelphia was 90º. Dew Points were in the mid 60s. Blue Bell on reached 86º.)
The heat dome is impressive on satellite imagery—
Water Vapor image shows the remnants of Hillary rotating around the large upper high pressure systems (heat dome) in the center of the country. The system in the Gulf is somewhat visible and the upper air support for the tropical system in the western Atlantic is also visible. (Click on image for a larger view.)
A sort of back door cold front (pushing in from the northeast) will suppress the heat dome to our south on Tuesday. Clouds in the morning Tuesday should break for partly to mostly sunny skies and cooler temperatures. Winds will shift to the NNE.
Several new things on the horizon—
Moisture rotating around the heat dome may bring us some showers Thursday into Friday.
A tropical system in the Gulf of Mexico will move westward, away from us, around the heat dome.
A tropical system looks like it will form in the western Atlantic somewhat near the Southeastern US. The path of this system is unknown at this time; it will likely remain offshore, but it may indirectly affect the Jersey shore within the week as its path bends north and northeastward.
Some of that Haze Monday is Smoke
Updated Mon 08/21 @ 9:16 AM — Today, some of that hazy sky isn’t only high cirrus clouds. It’s smoke and particulates, traveling across country over the northern edge of the ‘heat dome’ from Washington State Oregon and Canada. The haze/smoke layer is expected to thicken here about 4 PM—
HRRR smoke forecast for 4 PM today. Contours are low level smoke. (Click on image for a larger view.)
Hot, hazy and humid today. The smoke could shave off a degree from the expected high temperature. 91º to 93º still expected.
Unfavorable Pattern for Rain
We’ve moved into an unfavorable pattern for any rain, at least through Thursday.
We’re still under a northwest cyclonic flow of drier air moving over the northern edge of the ‘heat dome’ that’s in the Central US—
GEFS forecast for Monday evening. The general flow is from the northwest around the heat dome (white arrows). While a cold front will move through late Monday night, we’re again in an unfavorable region of a jet streak for rain. Little if any rainfall is expected with this cold front. Note the orange “thickness line” which denotes the edge of tropical air around the heat dome. It just moves through our area on Monday, only to be pushed back southwest. (Click on image for a larger view.)
The remnants of Hillary may bring much needed rain to NW parts of Canada as it flows due north and then bends towards us. We may see some of that moisture towards the end of this week.
Monday will be hot here with highs 90-93º—
NBM high temperatures Monday (standard deviation is 1.4º) (Click on image for a larger view.)
