NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260811_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 08/11 12Z 0.67 3020  90  50  11 0.00
Tue 08/11 13Z 0.64 3020  87  45  11 0.00
Tue 08/11 14Z 0.57 3020  81  43  12 0.01
Tue 08/11 15Z 0.62 3018  82  40  11 0.00
Tue 08/11 16Z 0.91 3017  81  33  11 0.00
Tue 08/11 17Z 3.52 3015  80  30  11 0.00
Tue 08/11 18Z 6.58 3014  77  33  12 0.00
Tue 08/11 19Z 6.65 3014  74  34  12 0.00
Tue 08/11 20Z 4.63 3013  72  36  12 0.00
Tue 08/11 21Z 2.83 3012  71  32  12 0.00
Tue 08/11 22Z 1.71 3012  71  35  12 0.00
Tue 08/11 23Z 1.07 2913  71  49  12 0.00
Wed 08/12 00Z 1.01 2914  72  61  12 0.00
Wed 08/12 01Z 0.88 2914  73  71  12 0.00
Wed 08/12 02Z 0.75 3014  74  67  12 0.00
Wed 08/12 03Z 0.62 3114  74  65  12 0.00
Wed 08/12 04Z 0.48 3113  76  57  12 0.00
Wed 08/12 05Z 0.43 3113  77  59  11 0.00
Wed 08/12 06Z 0.38 3111  78  60  11 0.00
Wed 08/12 07Z 0.36 3010  79  56  11 0.00
Wed 08/12 08Z 0.36 3010  79  45  11 0.00
Wed 08/12 09Z 0.37 3011  77  37  11 0.00
Wed 08/12 10Z 0.40 3012  78  34  11 0.00
Wed 08/12 11Z 0.40 3013  77  33  11 0.00
Wed 08/12 12Z 0.40 3113  76  39  11 0.00
Wed 08/12 13Z 0.32 3110  73  39  11 0.00
Wed 08/12 14Z 0.48 3009  74  47  11 0.00
Wed 08/12 15Z 1.24 3008  75  52  11 0.00
Wed 08/12 16Z 2.16 2907  73  55  11 0.00
Wed 08/12 17Z 3.50 2907  70  64  11 0.00
Wed 08/12 18Z 3.40 2807  70  70  12 0.01
Wed 08/12 19Z 2.52 2810  73  68  12 0.02
Wed 08/12 20Z 2.16 2710  77  67  12 0.00
Wed 08/12 21Z 2.17 2711  82  83  12 0.01
Wed 08/12 22Z 0.76 2812  82  64  12 0.03
Wed 08/12 23Z 0.66 2813  80  60  12 0.00
Thu 08/13 00Z 0.66 2913  84  64  11 0.00
Thu 08/13 01Z 0.62 2812  87  67  11 0.00
Thu 08/13 02Z 0.59 2811  87  68  11 0.00
Thu 08/13 03Z 0.51 2810  85  60  11 0.00
Thu 08/13 04Z 0.43 2809  84  67  11 0.00
Thu 08/13 05Z 0.36 2808  84  71  11 0.00
Thu 08/13 06Z 0.31 2808  82  71  11 0.00
Thu 08/13 07Z 0.28 2807  81  67  11 0.00
Thu 08/13 08Z 0.26 2807  79  67  11 0.00
Thu 08/13 09Z 0.30 2807  81  64  11 0.00
Thu 08/13 10Z 0.30 2708  86  73  10 0.01
Thu 08/13 11Z 0.24 2706  89  73  10 0.02
Thu 08/13 12Z 0.16 2704  89  71  10 0.01
Thu 08/13 13Z 0.15 2704  91  74  10 0.01
Thu 08/13 14Z 0.15 2903  92  72  10 0.01
Thu 08/13 15Z 0.19 2903  93  73  10 0.04
Thu 08/13 16Z 0.30 3005  92  67  10 0.05
Thu 08/13 17Z 0.38 3106  89  61  11 0.01
Thu 08/13 18Z 0.44 3106  84  63  11 0.00
Thu 08/13 19Z 1.01 3007  81  71  11 0.00
Thu 08/13 20Z 0.89 3108  79  71  11 0.00
Thu 08/13 21Z 0.60 3108  77  70  11 0.01
Thu 08/13 22Z 0.41 3111  81  81  11 0.04
Thu 08/13 23Z 0.46 3012  81  66  11 0.03

Run total areal avg QPF for the greens is: 0.32 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