Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260118_1800
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)
=== ===== === ==== ==== === === === ====
Sun 01/18 18Z 0.78 2409  87  60 -11 0.00
Sun 01/18 19Z 0.77 2307  84  64 -11 0.00
Sun 01/18 20Z 0.37 2405  81  69 -11 0.00
Sun 01/18 21Z 0.15 2302  79  67 -11 0.00
Sun 01/18 22Z 0.07 1901  79  66 -11 0.00
Sun 01/18 23Z 0.07 1900  79  66 -10 0.00
Mon 01/19 01Z 0.07 0400  83  76 -10 0.00
Mon 01/19 02Z 0.09 3401  84  77 -10 0.00
Mon 01/19 03Z 0.07 3403  85  74 -11 0.00
Mon 01/19 04Z 0.08 3405  88  68 -11 0.00
Mon 01/19 05Z 0.09 3405  90  65 -11 0.00
Mon 01/19 06Z 0.10 3405  92  55 -12 0.00
Mon 01/19 07Z 0.10 3305  93  36 -12 0.00
Mon 01/19 08Z 0.10 3104  93  36 -12 0.00
Mon 01/19 09Z 0.12 2903  93  33 -12 0.00
Mon 01/19 10Z 0.13 2703  93  30 -13 0.00
Mon 01/19 11Z 0.22 2605  94  26 -13 0.00
Mon 01/19 12Z 0.34 2508  93  31 -13 0.00
Mon 01/19 13Z 0.33 2409  90  38 -13 0.00
Mon 01/19 14Z 0.34 2309  89  51 -13 0.00
Mon 01/19 15Z 0.48 2211  92  68 -14 0.00
Mon 01/19 16Z 0.75 2113  91  78 -14 0.00
Mon 01/19 17Z 1.63 2215  86  77 -14 0.00
Mon 01/19 18Z 2.62 2214  77  75 -14 0.00
Mon 01/19 19Z 3.22 2215  78  77 -14 0.00
Mon 01/19 20Z 2.66 2216  84  84 -14 0.00
Mon 01/19 21Z 0.99 2219  89  85 -14 0.00
Mon 01/19 22Z 2.45 2323  92  79 -14 0.00
Mon 01/19 23Z 1.44 2425  91  75 -14 0.01
Tue 01/20 00Z 1.45 2427  91  70 -14 0.01
Tue 01/20 01Z 1.82 2428  88  69 -14 0.01
Tue 01/20 02Z 2.72 2431  86  64 -15 0.00
Tue 01/20 03Z 5.41 2431  79  62 -16 0.00
Tue 01/20 04Z 4.22 2432  71  57 -16 0.00
Tue 01/20 05Z 2.14 2434  78  62 -17 0.00
Tue 01/20 06Z 1.64 2533  79  59 -17 0.00
Tue 01/20 07Z 2.02 2531  85  50 -18 0.00
Tue 01/20 08Z 2.34 2530  90  56 -18 0.00
Tue 01/20 09Z 3.83 2530  89  54 -18 0.00
Tue 01/20 10Z 4.90 2629  81  47 -19 0.00
Tue 01/20 11Z 2.52 2627  74  43 -20 0.00
Tue 01/20 12Z 1.93 2625  71  40 -20 0.00
Tue 01/20 13Z 1.68 2624  71  44 -21 0.00
Tue 01/20 14Z 2.28 2621  71  45 -21 0.00
Tue 01/20 15Z 6.08 2619  71  57 -21 0.00
Tue 01/20 16Z 9.16 2617  72  71 -21 0.00
Tue 01/20 17Z 9.43 2517  76  73 -21 0.00
Tue 01/20 18Z 9.69 2518  79  71 -21 0.00
Tue 01/20 19Z 9.26 2519  78  71 -21 0.00
Tue 01/20 20Z 10.25 2521  75  72 -21 0.00
Tue 01/20 21Z 8.75 2623  78  70 -21 0.00
Tue 01/20 22Z 4.95 2624  82  58 -21 0.00
Tue 01/20 23Z 3.21 2625  80  45 -21 0.00
Wed 01/21 00Z 3.20 2625  82  42 -21 0.00
Wed 01/21 01Z 2.85 2626  81  48 -21 0.00
Wed 01/21 02Z 1.80 2727  75  52 -21 0.00
Wed 01/21 03Z 1.42 2727  74  51 -21 0.00
Wed 01/21 04Z 1.21 2726  74  52 -21 0.00
Wed 01/21 05Z 1.01 2725  73  50 -21 0.00

Run total areal avg QPF for the greens is: 0.03 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