NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20251229_1800
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)
=== ===== === ==== ==== === === === ====
Mon 12/29 18Z 0.33 2119  97  28   1 0.00
Mon 12/29 19Z 0.52 2221  96  20   0 0.01
Mon 12/29 20Z 0.60 2320  97  39   0 0.02
Mon 12/29 21Z 1.63 2625  96  88  -4 0.07
Mon 12/29 22Z 1.99 2725  93  93  -6 0.04
Mon 12/29 23Z 3.63 2627  86  66  -8 0.03
Tue 12/30 00Z 3.30 2627  82  68 -10 0.00
Tue 12/30 01Z 2.99 2526  85  60 -11 0.00
Tue 12/30 02Z 1.84 2525  82  49 -12 0.00
Tue 12/30 03Z 1.96 2527  88  67 -12 0.00
Tue 12/30 04Z 1.75 2526  90  63 -13 0.00
Tue 12/30 05Z 1.79 2527  92  70 -13 0.01
Tue 12/30 06Z 3.72 2627  86  77 -14 0.01
Tue 12/30 07Z 6.86 2629  83  79 -15 0.00
Tue 12/30 08Z 8.30 2729  79  76 -17 0.00
Tue 12/30 09Z 10.47 2829  78  79 -19 0.00
Tue 12/30 10Z 7.49 2828  78  78 -19 0.00
Tue 12/30 11Z 7.40 2828  78  76 -20 0.00
Tue 12/30 12Z 10.42 2829  77  72 -21 0.00
Tue 12/30 13Z 10.95 2827  77  75 -22 0.00
Tue 12/30 14Z 11.69 2827  78  76 -22 0.00
Tue 12/30 15Z 15.39 2828  78  67 -22 0.00
Tue 12/30 16Z 16.26 2727  78  68 -22 0.00
Tue 12/30 17Z 16.36 2727  77  71 -22 0.00
Tue 12/30 18Z 16.08 2727  77  73 -22 0.00
Tue 12/30 19Z 14.56 2727  78  76 -21 0.00
Tue 12/30 20Z 11.17 2727  80  77 -21 0.00
Tue 12/30 21Z 4.79 2728  81  78 -20 0.00
Tue 12/30 22Z 2.71 2730  82  77 -20 0.00
Tue 12/30 23Z 2.44 2731  83  75 -20 0.00
Wed 12/31 00Z 2.35 2732  84  73 -20 0.00
Wed 12/31 01Z 2.17 2732  85  72 -20 0.00
Wed 12/31 02Z 1.96 2732  87  69 -19 0.00
Wed 12/31 03Z 1.70 2732  88  61 -19 0.00
Wed 12/31 04Z 1.65 2732  89  52 -19 0.00
Wed 12/31 05Z 1.52 2733  88  39 -18 0.00
Wed 12/31 06Z 1.29 2733  83  19 -18 0.00
Wed 12/31 07Z 1.18 2732  79  10 -17 0.00
Wed 12/31 08Z 1.15 2732  74  16 -17 0.00
Wed 12/31 09Z 1.10 2732  68  25 -16 0.00
Wed 12/31 10Z 1.08 2732  67  40 -16 0.00
Wed 12/31 11Z 1.10 2631  74  55 -16 0.00
Wed 12/31 12Z 1.17 2629  80  65 -16 0.00
Wed 12/31 13Z 1.28 2628  85  70 -16 0.00
Wed 12/31 14Z 1.60 2526  89  70 -16 0.00
Wed 12/31 15Z 2.23 2523  91  72 -15 0.00
Wed 12/31 16Z 3.12 2421  92  74 -15 0.00
Wed 12/31 17Z 3.21 2419  93  75 -15 0.00
Wed 12/31 18Z 2.58 2319  92  77 -14 0.00
Wed 12/31 19Z 2.48 2319  92  80 -14 0.00
Wed 12/31 20Z 1.51 2218  93  81 -13 0.01
Wed 12/31 21Z 0.98 2118  93  82 -13 0.01
Wed 12/31 22Z 0.79 2120  92  80 -13 0.01
Wed 12/31 23Z 0.71 2121  92  78 -12 0.01
Thu 01/01 00Z 0.67 2122  93  81 -12 0.01
Thu 01/01 01Z 0.65 2122  93  87 -12 0.01
Thu 01/01 02Z 0.66 2123  93  85 -12 0.01
Thu 01/01 03Z 0.80 2123  95  85 -12 0.01
Thu 01/01 04Z 1.03 2324  96  78 -12 0.01
Thu 01/01 05Z 1.18 2720  95  75 -14 0.03

Run total areal avg QPF for the Central_Greens is: 0.31 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