THE FORECAST CITY MAP THEME

One way of drawing the weather

Every weather map on Forecast City, from a radar loop to a storm total, is drawn in one theme. The ground comes from the atlas, the colors are built so equal steps look equal, and the words use the site’s three typefaces. A Blend forecast and an MRMS radar mosaic should look like pages from the same book.

A light ground

Cream paper, never a black screen. Weather is drawn over the land and under the words, so the places always stay readable.

Equal steps look equal

Scales are blended in OKLab, a color space matched to how eyes judge lightness, so ten degrees looks like ten degrees anywhere on the scale.

Words, not codes

“Wednesday, 2 PM,” not “f054” or “18Z.” Observed and forecast are always labeled, and every map names its source.

The same twelve places

Each city picks a dozen places that appear on every map, with a value wherever the map has one, so two frames compare at a glance.

Anatomy of a map

Temperature, Wednesday 2 PM, as the player draws it

Forecast temperature for 2 PM Wednesday across metro Atlanta: 79 to 80 degrees downtown and to the southeast in orange, 70 to 71 degrees behind the line of storms to the northwest in pale tan, with a contour every 2 degrees.

1
Title cardWhat, when, and whether it happened. A solid chip means observed; a striped chip means forecast, the same as the timeline beneath the map.
2
Source stampEvery map names its source, run and lead time in plain words: “National Blend of Models · 8 AM Monday · 54 hours out.”
3
LegendThe scale and its unit, in the corner that covers the fewest places.
4
Value pillsBarlow Condensed on white, at the same twelve places on every map that has values to show.
5
ContoursTemperature gets a line every 2°, heavier at 60, 70, 80 and 90. Freezing is heaviest of all whenever it appears.
6
The groundThe atlas, turned down: rivers in blue, interstates in warm gray, city limits dashed. Weather over the land, under the words.

The color scales

One-hue scales run light to dark. Two-hue scales meet at a neutral middle. The gray strip under each bar is its lightness alone: if the order survives in gray, it survives for color-blind readers, on paper and on a phone in the sun.

TWO HUES · DIVERGING

Temperature

Temperature, feels-like, highs and lows. °F.

02032405060708090100

Centered on 60°F, the mild middle, and lightest there. Blues get darker as it gets colder, oranges and reds as it gets hotter. 32°F is drawn as a heavy line.

TWO HUES · DIVERGING

Warmer or cooler

Change since yesterday, difference from normal, the heat island. °F.

−6−4−20+2+4+6

Blue cooler, orange warmer, a neutral gray at zero, so “no change” looks like nothing at all.

ONE HUE · SEQUENTIAL

Dew point

How the air feels. °F.

3040505560657075

The bands match the comfort meter on every city page: dry, comfortable, sticky, muggy, oppressive.

ONE HUE · SEQUENTIAL

Wind and gusts

Sustained wind and peak gusts. mph.

010203040506070

Light to dark in one blue-violet. Streamlines on top show where the air is going; the color shows how hard it hits.

CONVENTION · RADAR

Radar: rain

Reflectivity from MRMS and the RRFS. dBZ.

15203040506070

The one scale that keeps tradition: the greens, yellows, reds and purples people already know, retuned for a light page. The jump to yellow at 40 dBZ marks heavy rain on purpose.

ONE HUE EACH · SEQUENTIAL

Radar: snow and ice

Where the Blend’s precipitation type says snow, sleet or freezing rain. dBZ.

Snow

10203040

Sleet and freezing rain

102540

Snow in blues, sleet and freezing rain in pinks, each light to dark, so a winter storm’s rain, ice and snow bands read apart at a glance.

ONE HUE · STEPPED

Rain total

Measured and forecast rain over a period. Inches.

.01.1.25.5.7511.5234

Evenly spaced steps at the amounts people plan around, so a tenth of an inch gets as much room as the difference between 3 and 4 inches. Nothing under a hundredth is drawn.

ONE HUE · SEQUENTIAL

Chance

Chance of rain, thunder or snow. Percent.

1030507090

One blue from pale to deep. Under 10% is left clear, so a map of low odds looks mostly empty, which it should.

Two grounds, one projection

The weather ground is the atlas plate with the volume turned down. Same projection, same scale, same roads and rivers, so any weather map lines up exactly with the city’s plate.

The atlas plate of central Atlanta: full-strength relief, the city filled in gold, blue and tan drainage basins split by the Eastern Continental Divide, red interstates and MARTA lines. — ATLAS GROUNDFull-strength relief and land color, drainage basins, transit and the BeltLine, interstates in red, the city filled in gold. Made to be looked at for its own sake.

The weather ground for metro Atlanta: faint shaded relief on cream, county lines, rivers in blue, interstates in warm gray with white casing, the city limits dashed, and twelve labeled places. — WEATHER GROUNDRelief at a little over half strength, no land color, no basins or transit. Interstates in warm gray with a white casing, rivers kept, the city limits dashed. Made to disappear under the weather.

Three typefaces, three jobs

SOURCE SERIF 4 · WHEN AND WHY Wednesday, 2 PM The line reaches downtown. The heaviest rain comes in its first 15 minutes. Valid times, headlines and the sentence that says what the map means.

OVERPASS · WHAT AND WHERE RADAR · FORECAST Sandy Springs RRFS simulated radar · 2 AM Monday run · 60 hours out The interface, place labels, legends and source stamps. The same face as the highway-sign type on the atlas.

BARLOW CONDENSED · HOW MUCH

79° 16 g25 .62″

0 1 2 3 4 5 6 7 8 9 Every number on a map, in a white pill with an ink edge, so it reads on any color underneath.

What’s in, and what isn’t

Four layers, chosen because each answers a question people actually ask: is it raining, what should I wear, will the wind knock things over, how much rain fell or will fall. Plus one map a day picked for the story it tells.

IN THE MAP ROOM

LAYERPAST 24 HOURSNEXT 3 DAYSGRID

RadarMRMS mosaic, every 2 minutesRRFS simulated radar1 km · 3 km

TemperatureRTMA rapid update, then URMANational Blend (the start of the NWS’s NDFD grids)2.5 km

Wind gustsRTMA rapid update, then URMARRFS 10 m wind and gusts2.5 km · 3 km

Rain totalMRMS multi-sensor: first pass, then the secondNational Blend1 km · 2.5 km

Pick of the dayA heat island, a first freeze, a snow line: whatever tells the day’s storyAny source aboveas drawn

ON FORECAST EAGLE INSTEAD

Upper-air charts: 500 mb heights and vorticity, jet streams
Instability and shear: CAPE, helicity, lapse rates
Soundings and hodographs
Model against model: RRFS, HRRR, GFS, ECMWF
Ensemble spread, plumes and probabilities
Every NBM and NDFD element, at every percentile

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THE RULE If a map needs a meteorologist to read it, it belongs on Forecast Eagle.