NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250501_1200
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 05/01 12Z 0.16 3006  32  13   3 0.00
Thu 05/01 13Z 0.18 3007  33  11   3 0.00
Thu 05/01 14Z 0.17 3006  36   9   3 0.00
Thu 05/01 15Z 0.14 2804  38   7   3 0.00
Thu 05/01 16Z 0.14 2303  42   5   3 0.00
Thu 05/01 17Z 0.26 2204  45   4   3 0.00
Thu 05/01 18Z 0.29 2203  44   4   4 0.00
Thu 05/01 19Z 0.20 2104  44   5   5 0.00
Thu 05/01 20Z 0.16 2004  43   7   5 0.00
Thu 05/01 21Z 0.08 2004  41   7   6 0.00
Thu 05/01 22Z 0.10 1806  40   8   7 0.00
Thu 05/01 23Z 0.13 1709  37  13   7 0.00
Fri 05/02 00Z 0.14 1711  34  39   8 0.00
Fri 05/02 01Z 0.14 1815  34  76   8 0.00
Fri 05/02 02Z 0.13 1818  40  95   8 0.00
Fri 05/02 03Z 0.07 1921  52  98   8 0.00
Fri 05/02 04Z 0.18 1823  73  97   7 0.02
Fri 05/02 05Z 0.16 1828  79  96   8 0.05
Fri 05/02 06Z 0.09 1929  80  94   9 0.06
Fri 05/02 07Z 0.08 2033  91  95   9 0.17
Fri 05/02 08Z 0.10 2032  90  85  10 0.06
Fri 05/02 09Z 0.09 2030  93  85  11 0.01
Fri 05/02 10Z 0.09 2028  93  83  11 0.01
Fri 05/02 11Z 0.10 2029  96  89  11 0.01
Fri 05/02 12Z 0.23 2228  97  95  10 0.07
Fri 05/02 13Z 0.31 2325  98  96   9 0.08
Fri 05/02 14Z 0.34 2322  94  92   9 0.06
Fri 05/02 15Z 0.37 2322  94  43   9 0.00
Fri 05/02 16Z 0.45 2422  91  61   9 0.00
Fri 05/02 17Z 0.60 2422  92  63   9 0.00
Fri 05/02 18Z 0.78 2420  91  61   9 0.00
Fri 05/02 19Z 2.35 2422  93  78   9 0.00
Fri 05/02 20Z 1.51 2321  92  42   9 0.00
Fri 05/02 21Z 1.61 2321  92  42   9 0.00
Fri 05/02 22Z 2.58 2423  88  56   9 0.01
Fri 05/02 23Z 0.98 2425  84  38  10 0.01
Sat 05/03 00Z 0.86 2527  83  65  10 0.00
Sat 05/03 01Z 0.81 2429  79  47  10 0.00
Sat 05/03 02Z 0.83 2529  78  24  10 0.00
Sat 05/03 03Z 1.05 2529  84  29   8 0.00
Sat 05/03 04Z 0.98 2527  87  12   7 0.00
Sat 05/03 05Z 1.02 2525  94  18   6 0.00
Sat 05/03 06Z 1.02 2525  96  35   6 0.01
Sat 05/03 07Z 0.77 2621  98  29   5 0.03
Sat 05/03 08Z 0.62 2621  96  30   5 0.02
Sat 05/03 09Z 0.48 2621  92  21   5 0.02
Sat 05/03 10Z 0.45 2721  91  19   4 0.01
Sat 05/03 11Z 0.41 2720  81  23   4 0.01
Sat 05/03 12Z 0.41 2721  76  28   4 0.01
Sat 05/03 13Z 0.37 2719  70  56   5 0.00
Sat 05/03 14Z 0.33 2816  66  78   5 0.00
Sat 05/03 15Z 0.31 2714  64  69   5 0.00
Sat 05/03 16Z 0.23 2810  60  85   5 0.00
Sat 05/03 17Z 0.20 2608  61  84   4 0.00
Sat 05/03 18Z 0.23 2608  63  95   4 0.00
Sat 05/03 19Z 0.22 2608  76  99   3 0.01
Sat 05/03 20Z 0.18 2508  84  98   4 0.02
Sat 05/03 21Z 0.17 2508  83  99   4 0.02
Sat 05/03 22Z 0.16 2607  90  97   4 0.11
Sat 05/03 23Z 0.15 2606  87  92   5 0.03

Run total areal avg QPF for the Northern_Greens is: 0.92 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