NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260811_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)
=== ===== === ==== ==== === === === ====
Tue 08/11 12Z 0.58 3019  92  46  11 0.00
Tue 08/11 13Z 0.56 3020  91  42  11 0.00
Tue 08/11 14Z 0.48 3019  82  42  12 0.01
Tue 08/11 15Z 0.51 3018  80  39  12 0.00
Tue 08/11 16Z 0.66 3016  82  30  12 0.00
Tue 08/11 17Z 3.00 3014  81  26  12 0.00
Tue 08/11 18Z 4.95 3013  78  25  12 0.00
Tue 08/11 19Z 4.87 3013  75  26  12 0.00
Tue 08/11 20Z 3.46 3111  73  30  13 0.00
Tue 08/11 21Z 1.99 3111  72  24  13 0.00
Tue 08/11 22Z 1.26 3010  72  29  13 0.00
Tue 08/11 23Z 0.77 2911  72  52  13 0.00
Wed 08/12 00Z 0.65 2912  73  68  13 0.00
Wed 08/12 01Z 0.60 2911  73  77  12 0.00
Wed 08/12 02Z 0.51 3011  72  66  12 0.00
Wed 08/12 03Z 0.47 3112  72  63  12 0.00
Wed 08/12 04Z 0.34 3212  74  56  12 0.00
Wed 08/12 05Z 0.32 3111  75  61  12 0.00
Wed 08/12 06Z 0.29 3110  77  60  11 0.00
Wed 08/12 07Z 0.30 3010  78  60  11 0.00
Wed 08/12 08Z 0.30 3010  77  47  11 0.00
Wed 08/12 09Z 0.30 3011  77  38  11 0.00
Wed 08/12 10Z 0.31 3012  78  31  11 0.00
Wed 08/12 11Z 0.30 3112  78  28  11 0.00
Wed 08/12 12Z 0.30 3112  76  32  11 0.00
Wed 08/12 13Z 0.22 3209  73  32  11 0.00
Wed 08/12 14Z 0.38 3108  74  37  11 0.00
Wed 08/12 15Z 1.22 3107  73  41  11 0.00
Wed 08/12 16Z 1.87 3006  70  47  11 0.00
Wed 08/12 17Z 2.38 3006  66  54  12 0.00
Wed 08/12 18Z 2.83 2906  65  59  12 0.00
Wed 08/12 19Z 2.76 2707  70  65  12 0.00
Wed 08/12 20Z 2.67 2708  73  61  12 0.00
Wed 08/12 21Z 2.78 2609  81  89  12 0.01
Wed 08/12 22Z 0.71 2712  85  67  12 0.04
Wed 08/12 23Z 0.54 2812  83  63  12 0.00
Thu 08/13 00Z 0.53 2912  87  72  12 0.00
Thu 08/13 01Z 0.51 2811  87  73  11 0.00
Thu 08/13 02Z 0.51 2811  86  72  11 0.00
Thu 08/13 03Z 0.45 2810  83  66  12 0.00
Thu 08/13 04Z 0.40 2709  81  76  12 0.00
Thu 08/13 05Z 0.36 2709  81  82  12 0.00
Thu 08/13 06Z 0.31 2708  79  83  12 0.00
Thu 08/13 07Z 0.29 2808  76  71  12 0.00
Thu 08/13 08Z 0.26 2807  75  71  12 0.00
Thu 08/13 09Z 0.31 2808  77  70  11 0.00
Thu 08/13 10Z 0.33 2609  87  82  11 0.02
Thu 08/13 11Z 0.24 2607  90  79  11 0.03
Thu 08/13 12Z 0.15 2604  91  77  10 0.01
Thu 08/13 13Z 0.13 2704  93  84  10 0.02
Thu 08/13 14Z 0.11 2803  95  81  10 0.02
Thu 08/13 15Z 0.12 2903  95  78  10 0.07
Thu 08/13 16Z 0.15 3004  94  71  11 0.07
Thu 08/13 17Z 0.16 3106  90  61  11 0.02
Thu 08/13 18Z 0.22 3106  85  61  11 0.00
Thu 08/13 19Z 0.62 3107  82  66  11 0.00
Thu 08/13 20Z 0.42 3108  77  68  12 0.00
Thu 08/13 21Z 0.32 3108  75  71  12 0.01
Thu 08/13 22Z 0.35 3111  78  82  11 0.04
Thu 08/13 23Z 0.35 3112  78  61  11 0.02

Run total areal avg QPF for the Central_Greens is: 0.39 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