NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260509_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 05/09 00Z 0.82 2510  71  79  -1 0.00
Sat 05/09 03Z 0.99 2515  56  64   0 0.00
Sat 05/09 06Z 1.15 2716  42  48  -1 0.00
Sat 05/09 09Z 0.57 2711  43  35   0 0.00
Sat 05/09 12Z 0.21 2009  45  42   0 0.00
Sat 05/09 15Z 0.61 1612  52  50   0 0.00
Sat 05/09 18Z 1.66 1616  73  74   1 0.03
Sat 05/09 21Z 0.19 1618  90  75   1 0.12
Sun 05/10 00Z 0.06 1818  96  49   3 0.02
Sun 05/10 03Z 0.15 1920  95  34   4 0.00
Sun 05/10 06Z 0.46 2127  95  29   4 0.00
Sun 05/10 09Z 0.60 2229  92  89   5 0.00
Sun 05/10 12Z 0.77 2328  91  47   4 0.00
Sun 05/10 15Z 1.75 2322  89  75   3 0.00
Sun 05/10 18Z 11.56 2418  78  68   3 0.00
Sun 05/10 21Z 13.49 2519  59  70   4 0.00
Mon 05/11 00Z 2.46 2719  57  35   2 0.00
Mon 05/11 03Z 0.86 2916  57  44   0 0.00
Mon 05/11 06Z 0.41 3011  67  63   0 0.00
Mon 05/11 09Z 0.31 2908  71  41  -1 0.00
Mon 05/11 12Z 0.17 3005  77  38  -2 0.00
Mon 05/11 15Z 0.94 3102  80  43  -2 0.00
Mon 05/11 18Z 1.92 3305  68  50   0 0.00
Mon 05/11 21Z 0.23 3204  75  44  -1 0.00
Tue 05/12 00Z 0.36 3411  66  82   0 0.00
Tue 05/12 03Z 0.10 3514  64  83  -1 0.00
Tue 05/12 06Z 0.14 3515  62  83  -1 0.00
Tue 05/12 09Z 0.10 3515  66  81  -1 0.00
Tue 05/12 12Z 0.19 3311  70  70  -2 0.00

Run total areal avg QPF for the greens is: 0.17 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