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Excessive Rainfall and Potential Tropical Cyclone in the South; Severe Thunderstorms in the Midwest

Excessive rainfall may produce locally considerable flash flooding over parts of the northwestern Gulf Coast, lower Mississippi River Valley, and Deep South through Thursday. Potential Tropical Cyclone One is forecast to become a tropical storm (Arthur) as it moves along or just off the northwestern Gulf coast through Wednesday. An outbreak of severe weather is forecast in the Midwest Wednesday. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260617_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 06/17 06Z 0.43 2311  76  46   9 0.00
Wed 06/17 07Z 0.48 2211  76  49   9 0.00
Wed 06/17 08Z 0.41 2210  74  51   9 0.00
Wed 06/17 09Z 0.34 2109  70  52   9 0.00
Wed 06/17 10Z 0.32 2109  69  53   9 0.00
Wed 06/17 11Z 0.29 2109  68  50   9 0.00
Wed 06/17 12Z 0.22 2007  67  51   9 0.00
Wed 06/17 13Z 0.23 1907  67  59   9 0.00
Wed 06/17 14Z 0.36 1807  68  71   9 0.00
Wed 06/17 15Z 0.50 1707  68  76  10 0.00
Wed 06/17 16Z 0.77 1808  72  70  10 0.02
Wed 06/17 17Z 0.92 1809  72  55  10 0.02
Wed 06/17 18Z 0.70 1809  74  60  10 0.02
Wed 06/17 19Z 1.52 1910  73  67  10 0.03
Wed 06/17 20Z 0.66 1808  72  78  10 0.01
Wed 06/17 21Z 0.28 1710  70  76  11 0.00
Wed 06/17 22Z 0.73 1811  70  73  11 0.00
Wed 06/17 23Z 0.49 1813  73  70  11 0.00
Thu 06/18 00Z 0.38 1815  75  59  11 0.00
Thu 06/18 01Z 0.60 2018  78  50  11 0.00
Thu 06/18 02Z 0.53 2019  85  39  11 0.00
Thu 06/18 03Z 0.51 2021  88  33  11 0.00
Thu 06/18 04Z 0.42 2018  87  67  11 0.00
Thu 06/18 05Z 0.38 2018  83  51  11 0.00
Thu 06/18 06Z 0.38 2020  83  54  11 0.00
Thu 06/18 07Z 0.43 2022  88  72  11 0.00
Thu 06/18 08Z 0.31 1923  89  91  11 0.01
Thu 06/18 09Z 0.30 1926  91  76  11 0.03
Thu 06/18 10Z 0.25 1827  90  68  12 0.02
Thu 06/18 11Z 0.29 1929  93  91  12 0.01
Thu 06/18 12Z 0.24 1832  84  92  13 0.01
Thu 06/18 13Z 0.20 1835  87  73  13 0.02
Thu 06/18 14Z 0.13 1741  87  83  14 0.01
Thu 06/18 15Z 0.24 1843  95  95  13 0.05
Thu 06/18 16Z 0.33 1841  96  98  13 0.10
Thu 06/18 17Z 0.38 1838  98  92  13 0.29
Thu 06/18 18Z 0.46 1935  97  90  14 0.13
Thu 06/18 19Z 0.54 1932  95  65  14 0.06
Thu 06/18 20Z 0.76 2030  95  63  14 0.05
Thu 06/18 21Z 0.98 2323  96  87  14 0.11
Thu 06/18 22Z 1.10 2526  83  32  14 0.15
Thu 06/18 23Z 1.48 2426  89  42  12 0.00
Fri 06/19 00Z 1.73 2429  93  57  12 0.01
Fri 06/19 01Z 1.96 2533  91  63  10 0.05
Fri 06/19 02Z 1.73 2533  90  64   9 0.02
Fri 06/19 03Z 1.49 2532  95  65   8 0.01
Fri 06/19 04Z 1.33 2532  96  68   7 0.02
Fri 06/19 05Z 1.22 2632  97  68   7 0.02
Fri 06/19 06Z 1.19 2632  96  66   7 0.02
Fri 06/19 07Z 1.02 2632  95  66   7 0.01
Fri 06/19 08Z 0.95 2633  92  67   8 0.01
Fri 06/19 09Z 0.91 2634  90  65   9 0.01
Fri 06/19 10Z 0.91 2634  91  59   9 0.01
Fri 06/19 11Z 0.90 2633  92  60   9 0.01
Fri 06/19 12Z 0.92 2633  92  56   9 0.01
Fri 06/19 13Z 0.96 2632  92  61   9 0.01
Fri 06/19 14Z 1.06 2631  92  54   9 0.01
Fri 06/19 15Z 1.13 2629  90  47   9 0.01
Fri 06/19 16Z 1.37 2627  91  42   9 0.00
Fri 06/19 17Z 2.59 2526  92  44   8 0.00

Run total areal avg QPF for the Central_Greens is: 1.39 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1