NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260214_0600
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 02/14 06Z 0.42 2616  74  62 -10 0.00
Sat 02/14 07Z 0.54 2719  79  62 -11 0.00
Sat 02/14 08Z 0.53 2819  83  63 -11 0.00
Sat 02/14 09Z 0.53 2817  87  69 -11 0.00
Sat 02/14 10Z 0.55 2917  88  77 -11 0.00
Sat 02/14 11Z 0.52 2816  90  79 -11 0.00
Sat 02/14 12Z 0.51 2817  93  79 -11 0.00
Sat 02/14 13Z 0.52 2817  93  74 -11 0.01
Sat 02/14 14Z 0.55 2818  94  69 -11 0.01
Sat 02/14 15Z 0.58 2818  95  61 -11 0.00
Sat 02/14 16Z 0.60 2917  96  49 -11 0.00
Sat 02/14 17Z 0.66 2916  95  38 -11 0.00
Sat 02/14 18Z 0.77 2916  94  29 -10 0.00
Sat 02/14 19Z 0.78 2817  94  24 -10 0.00
Sat 02/14 20Z 0.82 2818  95  23 -10 0.00
Sat 02/14 21Z 0.93 2819  95  22 -10 0.00
Sat 02/14 22Z 0.94 2820  93  21 -10 0.01
Sat 02/14 23Z 0.88 2921  89  18 -10 0.01
Sun 02/15 00Z 0.68 3022  82  17 -10 0.01
Sun 02/15 01Z 0.64 3022  77  16 -10 0.00
Sun 02/15 02Z 0.69 3023  75  16 -11 0.00
Sun 02/15 03Z 0.64 3023  71  15 -11 0.00
Sun 02/15 04Z 0.60 3023  70  15 -11 0.00
Sun 02/15 05Z 0.56 3023  73  15 -11 0.00
Sun 02/15 06Z 0.51 3023  74  15 -12 0.00
Sun 02/15 07Z 0.47 3023  73  16 -12 0.00
Sun 02/15 08Z 0.41 3123  70  17 -11 0.00
Sun 02/15 09Z 0.35 3122  68  18 -11 0.00
Sun 02/15 10Z 0.30 3121  61  18 -11 0.00
Sun 02/15 11Z 0.23 3220  50  18 -11 0.00
Sun 02/15 12Z 0.16 3319  41  17 -10 0.00
Sun 02/15 13Z 0.11 3417  31  17  -9 0.00
Sun 02/15 14Z 0.08 0013  23  17  -8 0.00
Sun 02/15 15Z 0.09 0210  22  19  -8 0.00
Sun 02/15 16Z 0.11 0308  23  24  -7 0.00
Sun 02/15 17Z 0.13 0607  25  30  -7 0.00
Sun 02/15 18Z 0.14 0806  27  37  -7 0.00
Sun 02/15 19Z 0.14 1006  29  41  -7 0.00
Sun 02/15 20Z 0.12 1206  29  43  -7 0.00
Sun 02/15 21Z 0.09 1406  28  45  -6 0.00
Sun 02/15 22Z 0.08 1508  25  46  -6 0.00
Sun 02/15 23Z 0.06 1610  23  40  -5 0.00
Mon 02/16 00Z 0.04 1711  23  37  -5 0.00
Mon 02/16 01Z 0.03 1711  25  42  -5 0.00
Mon 02/16 02Z 0.02 1712  29  51  -5 0.00
Mon 02/16 03Z 0.03 1812  35  52  -5 0.00
Mon 02/16 04Z 0.05 1813  44  56  -6 0.00
Mon 02/16 05Z 0.05 1813  58  72  -6 0.00
Mon 02/16 06Z 0.05 1912  71  80  -5 0.00
Mon 02/16 08Z 0.05 1911  84  91  -5 0.00
Mon 02/16 09Z 0.06 1910  86  93  -5 0.00
Mon 02/16 10Z 0.05 1909  87  90  -5 0.00
Mon 02/16 11Z 0.05 1908  86  88  -5 0.00
Mon 02/16 12Z 0.04 1809  85  84  -5 0.00
Mon 02/16 13Z 0.04 1809  84  84  -5 0.00
Mon 02/16 14Z 0.04 1809  84  82  -5 0.00
Mon 02/16 15Z 0.06 1909  84  82  -5 0.00
Mon 02/16 16Z 0.05 1909  84  79  -5 0.00
Mon 02/16 17Z 0.07 1909  83  67  -5 0.00

Run total areal avg QPF for the greens is: 0.05 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