NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260926_0000
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)
=== ===== === ==== ==== === === === ====
Sat 09/26 00Z 0.68 0416  74  14   9 0.00
Sat 09/26 01Z 0.73 0518  75  14   9 0.00
Sat 09/26 02Z 0.73 0519  73  13   9 0.00
Sat 09/26 03Z 0.78 0519  72  10   9 0.00
Sat 09/26 04Z 0.99 0622  70   8   9 0.00
Sat 09/26 05Z 1.28 0725  68   8   8 0.00
Sat 09/26 06Z 1.36 0725  67   8   8 0.00
Sat 09/26 07Z 1.19 0725  66   7   8 0.00
Sat 09/26 08Z 1.03 0624  65   6   8 0.00
Sat 09/26 09Z 0.93 0625  63   5   8 0.00
Sat 09/26 10Z 0.87 0625  62   5   8 0.00
Sat 09/26 11Z 0.86 0626  63   5   8 0.00
Sat 09/26 12Z 0.91 0627  63  10   8 0.00
Sat 09/26 13Z 0.93 0627  63   8   7 0.00
Sat 09/26 14Z 0.92 0627  58  10   8 0.00
Sat 09/26 15Z 0.88 0525  55  13   8 0.00
Sat 09/26 16Z 0.89 0523  53  17   8 0.00
Sat 09/26 17Z 1.55 0521  53  21   8 0.00
Sat 09/26 18Z 1.96 0421  55  25   8 0.00
Sat 09/26 19Z 2.16 0422  56  24   8 0.00
Sat 09/26 20Z 1.45 0424  56  31   8 0.00
Sat 09/26 21Z 1.61 0427  57  48   8 0.00
Sat 09/26 22Z 1.25 0428  54  43   8 0.00
Sat 09/26 23Z 1.26 0429  53  52   8 0.00
Sun 09/27 00Z 1.36 0530  54  62   8 0.00
Sun 09/27 01Z 1.38 0532  54  58   7 0.00
Sun 09/27 02Z 1.52 0533  62  65   7 0.00
Sun 09/27 03Z 1.01 0535  69  74   7 0.01
Sun 09/27 04Z 0.94 0537  74  81   8 0.01
Sun 09/27 05Z 0.92 0538  71  86   8 0.01
Sun 09/27 06Z 1.00 0638  73  90   7 0.01
Sun 09/27 07Z 0.97 0637  80  90   7 0.02
Sun 09/27 08Z 0.83 0638  87  87   9 0.06
Sun 09/27 09Z 0.72 0638  90  87  10 0.06
Sun 09/27 10Z 0.69 0638  91  85  10 0.04
Sun 09/27 11Z 0.66 0638  93  71  11 0.02
Sun 09/27 12Z 0.67 0738  93  67  11 0.04
Sun 09/27 13Z 0.70 0740  91  63  12 0.06
Sun 09/27 14Z 0.73 0742  90  67  12 0.05
Sun 09/27 15Z 0.75 0841  89  74  12 0.07
Sun 09/27 16Z 0.81 0842  91  75  12 0.07
Sun 09/27 17Z 0.80 0841  93  74  12 0.05
Sun 09/27 18Z 0.79 0940  92  71  12 0.04
Sun 09/27 19Z 0.80 0939  93  76  12 0.03
Sun 09/27 20Z 0.78 0938  94  75  12 0.03
Sun 09/27 21Z 0.78 0937  94  74  11 0.03
Sun 09/27 22Z 0.73 0937  94  72  12 0.02
Sun 09/27 23Z 0.72 1038  94  67  12 0.02
Mon 09/28 00Z 0.69 1038  94  71  12 0.03
Mon 09/28 01Z 0.66 1037  93  70  12 0.02
Mon 09/28 02Z 0.63 1036  94  72  12 0.02
Mon 09/28 03Z 0.60 1135  94  80  12 0.02
Mon 09/28 04Z 0.57 1133  93  82  12 0.02
Mon 09/28 05Z 0.55 1031  92  80  12 0.01
Mon 09/28 06Z 0.54 1031  92  80  12 0.01
Mon 09/28 07Z 0.52 1130  93  80  12 0.01
Mon 09/28 08Z 0.48 1128  92  83  12 0.02
Mon 09/28 09Z 0.47 1128  93  87  12 0.01
Mon 09/28 10Z 0.47 1127  92  88  12 0.01
Mon 09/28 11Z 0.44 1026  90  88  12 0.01

Run total areal avg QPF for the greens is: 0.94 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