NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260926_0000
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)
=== ===== === ==== ==== === === === ====
Sat 09/26 00Z 0.81 0416  71  14   9 0.00
Sat 09/26 01Z 0.83 0519  74  15   9 0.00
Sat 09/26 02Z 0.80 0519  74  13   9 0.00
Sat 09/26 03Z 0.84 0519  74  10   9 0.00
Sat 09/26 04Z 1.07 0623  73   7   9 0.00
Sat 09/26 05Z 1.32 0726  70   7   8 0.00
Sat 09/26 06Z 1.32 0727  68   7   8 0.00
Sat 09/26 07Z 1.14 0726  67   7   8 0.00
Sat 09/26 08Z 1.02 0626  65   6   8 0.00
Sat 09/26 09Z 0.96 0627  64   5   8 0.00
Sat 09/26 10Z 0.92 0627  65   5   8 0.00
Sat 09/26 11Z 0.90 0627  64   5   8 0.00
Sat 09/26 12Z 0.90 0628  63  12   8 0.00
Sat 09/26 13Z 0.86 0628  61   8   8 0.00
Sat 09/26 14Z 0.84 0627  55   9   8 0.00
Sat 09/26 15Z 0.83 0525  50  14   8 0.00
Sat 09/26 16Z 0.95 0524  50  21   8 0.00
Sat 09/26 17Z 2.13 0422  53  27   8 0.00
Sat 09/26 18Z 2.92 0422  54  33   8 0.00
Sat 09/26 19Z 3.20 0423  55  33   8 0.00
Sat 09/26 20Z 1.98 0426  54  45   8 0.00
Sat 09/26 21Z 2.20 0427  56  71   8 0.00
Sat 09/26 22Z 1.58 0428  53  64   8 0.00
Sat 09/26 23Z 1.54 0429  51  77   8 0.00
Sun 09/27 00Z 1.63 0530  54  85   7 0.00
Sun 09/27 01Z 1.68 0531  56  81   7 0.00
Sun 09/27 02Z 1.84 0533  67  90   6 0.00
Sun 09/27 03Z 1.03 0537  76  88   7 0.02
Sun 09/27 04Z 0.94 0539  82  90   7 0.02
Sun 09/27 05Z 0.98 0539  79  91   7 0.01
Sun 09/27 06Z 1.08 0539  82  90   7 0.01
Sun 09/27 07Z 0.97 0638  87  87   7 0.03
Sun 09/27 08Z 0.76 0638  93  82   9 0.07
Sun 09/27 09Z 0.70 0638  96  93  10 0.08
Sun 09/27 10Z 0.68 0638  96  90  10 0.06
Sun 09/27 11Z 0.66 0637  96  72  11 0.02
Sun 09/27 12Z 0.68 0638  96  70  11 0.06
Sun 09/27 13Z 0.72 0641  96  76  12 0.09
Sun 09/27 14Z 0.76 0743  95  82  12 0.08
Sun 09/27 15Z 0.77 0742  94  92  12 0.11
Sun 09/27 16Z 0.82 0844  96  92  12 0.10
Sun 09/27 17Z 0.81 0843  97  76  11 0.07
Sun 09/27 18Z 0.77 0942  97  72  12 0.05
Sun 09/27 19Z 0.77 0941  97  82  12 0.04
Sun 09/27 20Z 0.76 0940  97  83  12 0.04
Sun 09/27 21Z 0.76 0939  97  84  11 0.05
Sun 09/27 22Z 0.71 0937  97  80  11 0.04
Sun 09/27 23Z 0.71 0938  97  77  11 0.04
Mon 09/28 00Z 0.67 1038  97  78  12 0.05
Mon 09/28 01Z 0.62 1036  97  74  12 0.03
Mon 09/28 02Z 0.59 1035  97  80  11 0.03
Mon 09/28 03Z 0.56 1034  96  82  11 0.02
Mon 09/28 04Z 0.55 1034  96  82  12 0.02
Mon 09/28 05Z 0.53 1032  95  80  12 0.02
Mon 09/28 06Z 0.52 1031  95  84  12 0.02
Mon 09/28 07Z 0.49 1031  96  87  12 0.02
Mon 09/28 08Z 0.47 1030  96  90  12 0.02
Mon 09/28 09Z 0.48 1030  96  89  12 0.02
Mon 09/28 10Z 0.47 1029  96  90  12 0.02
Mon 09/28 11Z 0.45 1028  94  88  12 0.01

Run total areal avg QPF for the Central_Greens is: 1.37 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