Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260127_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)
=== ===== === ==== ==== === === === ====
Tue 01/27 00Z 0.52 3016  87  80 -17 0.00
Tue 01/27 01Z 0.57 3119  93  81 -19 0.00
Tue 01/27 02Z 0.79 3121  90  81 -20 0.01
Tue 01/27 03Z 0.66 3124  88  75 -20 0.01
Tue 01/27 04Z 0.55 3126  89  68 -20 0.00
Tue 01/27 05Z 0.54 3126  89  65 -21 0.00
Tue 01/27 06Z 0.62 3028  88  63 -21 0.00
Tue 01/27 07Z 0.65 3028  89  55 -21 0.00
Tue 01/27 08Z 0.65 3030  85  46 -21 0.00
Tue 01/27 09Z 0.58 3031  77  31 -21 0.00
Tue 01/27 10Z 0.53 3031  73  25 -20 0.00
Tue 01/27 11Z 0.47 3031  70  40 -20 0.00
Tue 01/27 12Z 0.47 3029  71  33 -19 0.00
Tue 01/27 13Z 0.43 3024  75  26 -19 0.00
Tue 01/27 14Z 0.38 2918  80  33 -19 0.00
Tue 01/27 15Z 0.43 2716  82  44 -19 0.00
Tue 01/27 16Z 0.48 2614  80  72 -19 0.00
Tue 01/27 17Z 0.52 2512  79  83 -19 0.00
Tue 01/27 18Z 0.84 2311  79  80 -19 0.00
Tue 01/27 19Z 1.15 2213  76  80 -18 0.00
Tue 01/27 20Z 4.21 2214  74  79 -19 0.00
Tue 01/27 21Z 1.68 2316  83  81 -19 0.00
Tue 01/27 22Z 1.13 2318  86  80 -19 0.00
Tue 01/27 23Z 2.18 2420  90  78 -19 0.01
Wed 01/28 00Z 1.97 2621  89  75 -20 0.01
Wed 01/28 01Z 0.98 2821  80  72 -20 0.00
Wed 01/28 02Z 0.85 2821  77  73 -20 0.00
Wed 01/28 03Z 0.65 2820  80  73 -19 0.00
Wed 01/28 04Z 0.59 2719  83  72 -19 0.01
Wed 01/28 05Z 0.68 2719  86  68 -20 0.01
Wed 01/28 06Z 0.67 2819  89  65 -20 0.01
Wed 01/28 07Z 0.63 2920  88  62 -20 0.00
Wed 01/28 08Z 0.56 2921  88  60 -20 0.00
Wed 01/28 09Z 0.53 2921  89  56 -20 0.00
Wed 01/28 10Z 0.46 3020  87  49 -19 0.00
Wed 01/28 11Z 0.39 3019  86  43 -19 0.00
Wed 01/28 12Z 0.39 3018  88  36 -19 0.00
Wed 01/28 13Z 0.38 3017  85  32 -19 0.00
Wed 01/28 14Z 0.38 2916  82  36 -19 0.00
Wed 01/28 15Z 0.42 2914  82  40 -19 0.00
Wed 01/28 16Z 0.52 2812  80  42 -19 0.00
Wed 01/28 17Z 0.93 2811  75  50 -19 0.00
Wed 01/28 18Z 1.34 2810  73  59 -19 0.00
Wed 01/28 19Z 1.13 2709  74  67 -18 0.00
Wed 01/28 20Z 1.06 2709  80  68 -18 0.00
Wed 01/28 21Z 0.70 2609  85  72 -18 0.00
Wed 01/28 22Z 0.64 2611  88  78 -18 0.00
Wed 01/28 23Z 0.61 2611  88  82 -18 0.00
Thu 01/29 00Z 0.58 2712  85  82 -18 0.00
Thu 01/29 01Z 0.55 2812  85  82 -18 0.00
Thu 01/29 02Z 0.48 2911  85  81 -18 0.00
Thu 01/29 03Z 0.39 3011  87  81 -18 0.01
Thu 01/29 04Z 0.34 3010  88  80 -18 0.01
Thu 01/29 05Z 0.33 3009  88  80 -18 0.01
Thu 01/29 06Z 0.32 3009  89  79 -18 0.01
Thu 01/29 07Z 0.29 3109  90  79 -19 0.01
Thu 01/29 08Z 0.28 3111  89  77 -19 0.01
Thu 01/29 09Z 0.23 3211  90  75 -19 0.00
Thu 01/29 10Z 0.18 3210  90  72 -19 0.00
Thu 01/29 11Z 0.19 3110  89  70 -19 0.00

Run total areal avg QPF for the Central_Greens is: 0.13 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