NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260405_1200
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)
=== ===== === ==== ==== === === === ====
Sun 04/05 12Z 0.30 2030  99  98   5 0.00
Sun 04/05 13Z 0.35 2128  98  96   6 0.06
Sun 04/05 14Z 0.41 2227  98  98   5 0.15
Sun 04/05 15Z 0.51 2327  98  97   5 0.16
Sun 04/05 16Z 0.51 2424  96  93   4 0.06
Sun 04/05 17Z 0.65 2525  95  84   2 0.02
Sun 04/05 18Z 0.72 2523  95  43   1 0.02
Sun 04/05 19Z 0.82 2623  96  30   0 0.01
Sun 04/05 20Z 1.10 2725  95  17   0 0.01
Sun 04/05 21Z 1.27 2724  95  14  -2 0.01
Sun 04/05 22Z 1.28 2724  94  10  -2 0.01
Sun 04/05 23Z 1.66 2626  92   9  -3 0.01
Mon 04/06 00Z 2.12 2728  86  10  -4 0.00
Mon 04/06 01Z 2.16 2728  86  16  -5 0.00
Mon 04/06 02Z 1.55 2729  86  25  -5 0.00
Mon 04/06 03Z 1.53 2730  89  30  -6 0.00
Mon 04/06 04Z 2.02 2732  93  32  -7 0.00
Mon 04/06 05Z 2.19 2732  94  32  -8 0.01
Mon 04/06 06Z 2.06 2732  92  35  -9 0.00
Mon 04/06 07Z 1.34 2831  92  42  -9 0.00
Mon 04/06 08Z 1.22 2832  94  51  -9 0.00
Mon 04/06 09Z 1.20 2831  93  54  -9 0.00
Mon 04/06 10Z 1.44 2831  94  55  -9 0.00
Mon 04/06 11Z 1.57 2929  96  56 -10 0.00
Mon 04/06 12Z 1.94 2926  96  59 -10 0.00
Mon 04/06 13Z 2.87 2925  95  67 -11 0.00
Mon 04/06 14Z 3.72 2824  95  71 -10 0.00
Mon 04/06 15Z 4.19 2823  93  73 -10 0.00
Mon 04/06 16Z 7.48 2822  90  72 -10 0.00
Mon 04/06 17Z 12.25 2822  84  72  -9 0.00
Mon 04/06 18Z 13.91 2821  77  72  -9 0.00
Mon 04/06 19Z 14.06 2721  74  73  -8 0.00
Mon 04/06 20Z 13.66 2720  73  81  -8 0.00
Mon 04/06 21Z 13.16 2820  72  80  -8 0.00
Mon 04/06 22Z 12.02 2821  73  79  -8 0.00
Mon 04/06 23Z 6.47 2821  74  75  -9 0.00
Tue 04/07 00Z 3.32 2821  76  74  -9 0.00
Tue 04/07 01Z 1.41 2819  82  76  -9 0.00
Tue 04/07 02Z 0.99 2818  89  79  -9 0.01
Tue 04/07 03Z 0.91 2919  90  80 -10 0.02
Tue 04/07 04Z 0.68 2917  90  79 -10 0.01
Tue 04/07 05Z 0.56 3015  91  83 -11 0.01
Tue 04/07 06Z 0.44 3113  90  87 -11 0.01
Tue 04/07 07Z 0.35 3112  85  85 -11 0.01
Tue 04/07 08Z 0.38 3112  84  88 -12 0.00
Tue 04/07 09Z 0.41 3013  86  87 -12 0.00
Tue 04/07 10Z 0.44 3013  90  75 -12 0.00
Tue 04/07 11Z 0.43 3013  92  75 -13 0.00
Tue 04/07 12Z 0.48 3013  94  75 -13 0.01
Tue 04/07 13Z 0.66 3013  91  71 -14 0.00
Tue 04/07 14Z 1.15 3013  85  61 -14 0.00
Tue 04/07 15Z 3.45 3013  81  47 -14 0.00
Tue 04/07 16Z 4.58 3013  77  28 -14 0.00
Tue 04/07 17Z 5.43 3013  74  21 -14 0.00
Tue 04/07 18Z 5.54 3013  71  10 -13 0.00
Tue 04/07 19Z 5.33 3013  66   9 -13 0.00
Tue 04/07 20Z 5.15 3013  60  12 -13 0.00
Tue 04/07 21Z 4.54 3013  55  19 -13 0.00
Tue 04/07 22Z 2.75 3013  52  27 -13 0.00
Tue 04/07 23Z 1.02 3014  48  32 -13 0.00

Run total areal avg QPF for the Central_Greens is: 0.61 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