Alert archive / New Hampshire / Flash Flood Warnings in 2021

Flash Flood Warning 14, NWS Gray, ME

July 29, 2021Hillsborough County, Rockingham County, New Hampshire

NWS Gray, ME issued this flash flood warning at Jul 29, 2021, 10:58 PM EDT for Hillsborough County, Rockingham County, New Hampshire. It was in force for 3 hr. 2 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Jul 29, 2021, 10:58 PM EDT (02:58 UTC)
Expired: Jul 30, 2021, 1:30 AM EDT
In force: 3 hr
Issued by: NWS Gray, ME
Area: Storm-based polygon
Flood severity: None

Counties Hillsborough County, NH, Rockingham County, NH

The radar

The Boston radar (KBOX), 102 km from the middle of the area, began a volume at 03:02 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What was reported inside it

Time	Report	Where	Remark
Jul 29, 11:29 PM EDT	FLASH FLOOD	2 Sse Bedford, NH	REPORT FROM MPING: RIVER/CREEK OVERFLOWING; CROPLAND/YARD/BASEMENT FLOODING.
Jul 29, 11:30 PM EDT	FLASH FLOOD	3 Nnw Hollis, NH	A FEW ROADS WASHED OUT IN HOLLIS WHERE APPROXIMATELY 2.5 INCHES OF RAIN FELL IN AN HOUR AND A HALF.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Gray, ME (KGYX), launched 00:00Z, 3.0 hours before the alert went out and 150 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 158 J/kg
Mixed-layer CIN: -1 J/kg
Mixed-layer LCL: 492 m above ground
0-6 km bulk shear: 40 kt
0-1 km storm-relative helicity: 63 m²/s²
0-3 km storm-relative helicity: 133 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.4

Open this sounding in Storm Lab

The text

As transmitted.

045 
WGUS51 KGYX 300258
FFWGYX
NHC011-015-300530-
/O.NEW.KGYX.FF.W.0014.210730T0258Z-210730T0530Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Gray ME
1058 PM EDT Thu Jul 29 2021

The National Weather Service in Gray has issued a

* Flash Flood Warning for...
  Southeastern Hillsborough County in southern New Hampshire...
  Southwestern Rockingham County in southern New Hampshire...

* Until 130 AM EDT.

* At 1058 PM EDT, Doppler radar and automated rain gauges indicated 
  thunderstorms producing heavy rain across the warned area. The 
  expected rainfall rate is 1 to 2 inches in 1 hour. Flash flooding 
  is ongoing or expected to begin shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar and automated gauges.

  IMPACT...Flash flooding of small creeks and streams, urban
           areas, highways, streets and underpasses as well as
           other poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Manchester, Nashua, Derry, Merrimack, Salem, Bedford, Milford, 
  Amherst, and Litchfield.

This includes the following highways...
	Interstate 293 between mile markers 1 and 7.
	Interstate 93 between mile markers 1 and 22.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Flooding is occurring or is imminent. It is important to know where 
you are relative to streams, rivers, or creeks which can become 
killers in heavy rains. Campers and hikers should avoid streams or 
creeks.

&&

LAT...LON 4298 7180 4300 7174 4300 7129 4280 7117
      4279 7119 4274 7118 4274 7125 4270 7129
      4271 7170

FLASH FLOOD...RADAR AND GAUGE INDICATED
EXPECTED RAINFALL...1-2 INCHES IN 1 HOUR

$$

MLE

The office that day

Everything else NWS Gray, ME issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 29, 8:35 PM EDT	Flash Flood Warning	GYX	Cheshire, Hillsborough, Merrimack, Sullivan	6 hr
Jul 29, 8:58 PM EDT	Areal Flood Advisory	GYX	Belknap, Carroll, Grafton, Hillsborough, Merrimack, Rockingham and 2 more	4 hr
Jul 29, 9:14 PM EDT	Special Weather Statement	GYX	Hillsborough	46 min
Jul 29, 9:33 PM EDT	Flash Flood Warning	GYX	Belknap, Carroll, Grafton, Merrimack, Rockingham, Strafford and 1 more	5 hr
Jul 29, 9:57 PM EDT	Special Weather Statement	GYX	Rockingham, Strafford	48 min
Jul 29, 10:32 PM EDT	Flash Flood Warning	GYX	Cheshire, Hillsborough	3 hr
Jul 29, 10:36 PM EDT	Areal Flood Advisory	GYX	Hillsborough, Merrimack, Rockingham	3 hr
Jul 30, 1:34 AM EDT	River Flood Warning	GYX	Merrimack	41 hr
Jul 30, 6:10 AM EDT	River Flood Warning	GYX	Merrimack	24 hr
Jul 30, 4:05 PM EDT	River Flood Warning	GYX	Merrimack	7 hr

Nearby

Flash Flood Warnings in New Hampshire, 2021 Every flash flood warning in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.