Not much to change. Will go with 4-6 inch storm fall totals for the triangle. Look for a bulls eye of precip well above three inches in the extreme southeast. The upslope regions may see a bit more as well. I don't see much of a break in the precip from beginning to end now due to the quick enhancement of the coastal low. It will almost be an immediate handoff from the 2 quasi seperate features mentioned earlier. Look for the precip to begin to wind down Thursday afternoon. Heaviest precip should be late tonight through tomorrow morning.
We're off to a pretty decent start already.. maybe moreso than the models were predicting so I wouldn't be shocked to see us in the 6+ range when all is said and done.
Tuesday, November 10, 2009
update on upcoming storm:
NAM now coming in even more bullish than the 6z GFS on precip amounts. So far it seems like a good call to go with the GFS yesterday. Despite the fact that this is an unusual storm, am now feeling extremely confident that we will see a historic storm in the triangle. Will post a quick update once the 12z GFS comes in.
November 09 heavy rain event
Potential historic rainfall event beginning this afternoon and lasting through mid week. Upwards of 5-7 inches could around and east of the triangle.
Moderate to heavy rain will begin later this afternoon into this evening as isentropic lift increases. Radar trends show showers already near the region. Expect these showers to increase in coverage and intensity as the right entrance region of an upper jet moves over the triangle region later this afternoon and through the night. The potential exists for one to two inches overnight as this feature moves through. Very slight lull in the heavy and widespread precip looks to occur tomorrow morning however, the rain will reintinsify Wednesday afternoon and through the night. In fact it appears that this has the potential to be the heaviest period of rain potentially dropping up to to 2 inches in a single 6 hour period Wednesday evening. This is due to a strong 500 mb vort max along with the emergence of the coastal low. This coastal low will continue to deepen due to strong diabatic influences and could deepen more than models are predicting. GFS predicts the precip to stick around through the day on Thursday despite the advance of cool dry air from the NW. It will be a figurative battle in regards to which air mass wins out... either the dry continental air or the moist tropical air. NAM finally starting to come into agreement with the GFS.
Now looking at statewide 3 inch storm total with 6-8 inches possible along the coastal plain. Will go ahead and call 4-5 inches storm total in the triangle region.
Wind also could be a major factor on Wednesday and Thursday as the Coastal low and Great Lakes High create an area of enhanced isobaric flow.
HPC is in genera agreement with a sharp cutoff in the western part of the state. I still think low level low will lead to enhanced precip due to orographic lift. RAH is less bullish on rainfall totals... but that may change later today.
Will try and update later today.
Moderate to heavy rain will begin later this afternoon into this evening as isentropic lift increases. Radar trends show showers already near the region. Expect these showers to increase in coverage and intensity as the right entrance region of an upper jet moves over the triangle region later this afternoon and through the night. The potential exists for one to two inches overnight as this feature moves through. Very slight lull in the heavy and widespread precip looks to occur tomorrow morning however, the rain will reintinsify Wednesday afternoon and through the night. In fact it appears that this has the potential to be the heaviest period of rain potentially dropping up to to 2 inches in a single 6 hour period Wednesday evening. This is due to a strong 500 mb vort max along with the emergence of the coastal low. This coastal low will continue to deepen due to strong diabatic influences and could deepen more than models are predicting. GFS predicts the precip to stick around through the day on Thursday despite the advance of cool dry air from the NW. It will be a figurative battle in regards to which air mass wins out... either the dry continental air or the moist tropical air. NAM finally starting to come into agreement with the GFS.
Now looking at statewide 3 inch storm total with 6-8 inches possible along the coastal plain. Will go ahead and call 4-5 inches storm total in the triangle region.
Wind also could be a major factor on Wednesday and Thursday as the Coastal low and Great Lakes High create an area of enhanced isobaric flow.
HPC is in genera agreement with a sharp cutoff in the western part of the state. I still think low level low will lead to enhanced precip due to orographic lift. RAH is less bullish on rainfall totals... but that may change later today.
Will try and update later today.
Monday, November 9, 2009
11/10-11/11 rainfal event
GFS and NAM both depict tropical storm Ida to come ashore late tonight/early tomorrow and interact with a strengthening short wave. A cold air damming high will move into the Great Lakes region as the storm slowly moves east along the Florida Peninsula. This sets up the potential for a significant overrunning event. Latest GFS Isentropic analysis supports this setup.
The NAM has recently trended away from high precip amounts... but I really like this setup for a heavy rain event. Cold dry air will filter in from the north, but it will basically be confined to the surface with warm moist tropical air advecting in strongly from the east just above the surface. I have doubts that the cold dry air at the surface will effect the precip that much if at all. It just looks like a classic setup to me even with the northerly surface winds. Normally I would be concerned about the NAM showing little precip for North Carolina... but in this case I'm quite confident that the GFS is correct. But with that in mind... we are talking about weather forecasting. Now... there will be a sharp cut off in the precip depending up the height of the column of dry air and the "reach" of the moist air. This boundary should be well to our north.
Expect widespread 2-3 inch rainfall amounts w/ potentially higher amounts near the foothills due to additional orographic lifting.
HPC outlook review: Basically 2-3 inch totals statewide except for the far northwest. The have the intensity increasing from NW to SE. This depiction does make some sense, although I am concerned a bit more with orographic effects.
RAH AFD review: RAH in basic agreement, but they do a nice job of mentioning the upper level features associated with the heavy rainfall including two instances of favorable jet dynamics due to the settling of the quasi irregular troughiness (i.e. merging of the deepening northern trough with the weakening southern trough.). Also, they point out the dynamic effect of latent heat release leading to an enhanced PV anomaly off the coast. This is the kicker for the enhanced rainfall along the coast. Will really need to keep an eye on this for some unexpected very rapid deepening which could lead to enhanced rain even for the triangle. Although, dry air should be pretty well mixed in through high enough in the column to keep the moisture off the coast. But again these thermodynamic effects need to be watched.
Forgot to mention the high wind potential Wednesday as the coastal develops. Could see some pretty good gusts with the high over the lakes and a deeping cyclone off the coast. This should be a fun storm.
The NAM has recently trended away from high precip amounts... but I really like this setup for a heavy rain event. Cold dry air will filter in from the north, but it will basically be confined to the surface with warm moist tropical air advecting in strongly from the east just above the surface. I have doubts that the cold dry air at the surface will effect the precip that much if at all. It just looks like a classic setup to me even with the northerly surface winds. Normally I would be concerned about the NAM showing little precip for North Carolina... but in this case I'm quite confident that the GFS is correct. But with that in mind... we are talking about weather forecasting. Now... there will be a sharp cut off in the precip depending up the height of the column of dry air and the "reach" of the moist air. This boundary should be well to our north.
Expect widespread 2-3 inch rainfall amounts w/ potentially higher amounts near the foothills due to additional orographic lifting.
HPC outlook review: Basically 2-3 inch totals statewide except for the far northwest. The have the intensity increasing from NW to SE. This depiction does make some sense, although I am concerned a bit more with orographic effects.
RAH AFD review: RAH in basic agreement, but they do a nice job of mentioning the upper level features associated with the heavy rainfall including two instances of favorable jet dynamics due to the settling of the quasi irregular troughiness (i.e. merging of the deepening northern trough with the weakening southern trough.). Also, they point out the dynamic effect of latent heat release leading to an enhanced PV anomaly off the coast. This is the kicker for the enhanced rainfall along the coast. Will really need to keep an eye on this for some unexpected very rapid deepening which could lead to enhanced rain even for the triangle. Although, dry air should be pretty well mixed in through high enough in the column to keep the moisture off the coast. But again these thermodynamic effects need to be watched.
Forgot to mention the high wind potential Wednesday as the coastal develops. Could see some pretty good gusts with the high over the lakes and a deeping cyclone off the coast. This should be a fun storm.
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