NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260117_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)
=== ===== === ==== ==== === === === ====
Sat 01/17 18Z 0.29 2118  96  86  -6 0.00
Sat 01/17 19Z 0.35 2119  96  87  -6 0.02
Sat 01/17 20Z 0.44 2219  97  86  -7 0.01
Sat 01/17 21Z 0.55 2420  97  82  -7 0.01
Sat 01/17 22Z 0.56 2520  94  78  -7 0.01
Sat 01/17 23Z 0.62 2521  93  72  -7 0.01
Sun 01/18 00Z 0.65 2622  91  57  -7 0.01
Sun 01/18 01Z 0.59 2621  86  59  -7 0.00
Sun 01/18 02Z 0.57 2521  84  49  -6 0.00
Sun 01/18 03Z 0.56 2521  87  41  -6 0.00
Sun 01/18 04Z 0.64 2423  89  46  -7 0.00
Sun 01/18 05Z 0.75 2425  94  48  -7 0.00
Sun 01/18 06Z 0.77 2424  94  42  -7 0.00
Sun 01/18 07Z 0.79 2423  94  25  -8 0.01
Sun 01/18 08Z 0.81 2424  94  32  -8 0.01
Sun 01/18 09Z 0.75 2423  92  60  -8 0.01
Sun 01/18 10Z 0.69 2421  91  65  -8 0.00
Sun 01/18 11Z 0.64 2420  87  86  -8 0.00
Sun 01/18 12Z 0.66 2319  91  88  -9 0.00
Sun 01/18 13Z 0.81 2319  93  83  -9 0.01
Sun 01/18 14Z 1.08 2420  96  74 -10 0.01
Sun 01/18 15Z 0.87 2418  97  66 -10 0.01
Sun 01/18 16Z 0.76 2417  97  64 -10 0.01
Sun 01/18 17Z 0.67 2415  96  62 -10 0.01
Sun 01/18 18Z 0.60 2413  94  69 -10 0.00
Sun 01/18 19Z 0.56 2412  90  68 -10 0.00
Sun 01/18 20Z 0.47 2510  89  70 -10 0.00
Sun 01/18 21Z 0.34 2607  88  67 -10 0.00
Sun 01/18 22Z 0.21 2505  85  86 -10 0.00
Sun 01/18 23Z 0.08 2301  82  79 -10 0.00
Mon 01/19 00Z 0.04 2300  84  73  -9 0.00
Mon 01/19 01Z 0.05 2801  86  71  -9 0.00
Mon 01/19 02Z 0.05 3202  86  84  -9 0.00
Mon 01/19 03Z 0.03 3202  87  82 -10 0.00
Mon 01/19 04Z 0.05 3203  87  85 -10 0.01
Mon 01/19 05Z 0.02 3404  89  87 -10 0.01
Mon 01/19 06Z 0.03 3404  91  86 -10 0.01
Mon 01/19 07Z 0.05 3204  92  78 -11 0.00
Mon 01/19 08Z 0.05 3103  92  62 -11 0.00
Mon 01/19 09Z 0.07 2702  93  49 -11 0.00
Mon 01/19 10Z 0.10 2503  92  39 -11 0.00
Mon 01/19 11Z 0.14 2405  92  34 -11 0.00
Mon 01/19 12Z 0.19 2307  92  40 -11 0.00
Mon 01/19 13Z 0.20 2208  91  46 -11 0.00
Mon 01/19 14Z 0.23 2110  91  71 -12 0.00
Mon 01/19 15Z 0.32 2112  91  86 -12 0.00
Mon 01/19 16Z 0.55 2215  92  87 -13 0.00
Mon 01/19 17Z 1.40 2215  90  81 -13 0.00
Mon 01/19 18Z 2.64 2217  88  77 -14 0.00
Mon 01/19 19Z 6.22 2319  89  80 -14 0.00
Mon 01/19 20Z 3.57 2321  90  80 -14 0.01
Mon 01/19 21Z 3.19 2423  92  77 -14 0.01
Mon 01/19 22Z 1.91 2425  85  71 -14 0.01
Mon 01/19 23Z 1.49 2427  86  67 -14 0.00
Tue 01/20 00Z 1.64 2329  87  65 -14 0.00
Tue 01/20 01Z 1.75 2431  85  63 -14 0.00
Tue 01/20 02Z 2.30 2433  87  57 -14 0.00
Tue 01/20 03Z 3.15 2433  89  49 -15 0.00
Tue 01/20 04Z 3.94 2433  85  51 -16 0.00
Tue 01/20 05Z 1.93 2434  87  77 -16 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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